Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2017	Mar. 05, 2018	Jun. 30, 2017
Document and Entity Information
Entity Registrant Name	Mistras Group, Inc.
Entity Central Index Key	0001436126
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Accelerated Filer
Entity Public Float			$ 377.7
Entity Common Stock, Shares Outstanding		28,301,598
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	FY

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current Assets
Cash and cash equivalents	$ 27,541	$ 19,154
Accounts receivable, net	138,080	130,852
Inventories	10,503	10,017
Deferred income taxes	0	6,230
Prepaid expenses and other current assets	18,884	16,399
Total current assets	195,008	182,652
Property, plant and equipment, net	87,143	73,149
Intangible assets, net	63,739	40,007
Goodwill	203,438	169,940
Deferred income taxes	1,606	1,086
Other assets	3,507	2,593
Total Assets	554,441	469,427
Current Liabilities
Accounts payable	10,362	6,805
Accrued expenses and other current liabilities	65,561	58,697
Current portion of long-term debt	2,358	1,379
Current portion of capital lease obligations	5,875	6,488
Income taxes payable	6,069	4,342
Total current liabilities	90,225	77,711
Long-term debt, net of current portion	164,520	85,917
Obligations under capital leases, net of current portion	8,738	9,682
Deferred income taxes	8,803	17,584
Other long-term liabilities	11,363	7,789
Total Liabilities	283,649	198,683
Commitments and contingencies
Equity
Preferred stock, 10,000,000 shares authorized	0	0
Common stock, $0.01 par value, 200,000,000 shares authorized, 28,294,968 and 29,216,745 shares issued	282	292
Additional paid-in capital	222,425	217,211
Treasury stock at cost, 0 and 420,258 shares	0	(9,000)
Retained earnings	64,717	91,803
Accumulated other comprehensive loss	(16,805)	(29,724)
Total Mistras Group, Inc. stockholders’ equity	270,619	270,582
Non-controlling interests	173	162
Total Equity	270,792	270,744
Total Liabilities and Equity	$ 554,441	$ 469,427

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Preferred stock, shares authorized (in shares)	10,000,000	10,000,000
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	200,000,000	200,000,000
Common stock, shares issued (in shares)	28,294,968	29,216,745
Treasury stock at cost (in shares)	0	420,258

Consolidated Statements of (Loss) Income - USD ($) shares in Thousands, $ in Thousands	7 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2017	May 31, 2016	May 31, 2015
Income Statement [Abstract]
Revenue	$ 404,161	$ 700,970	$ 719,181	$ 711,252
Cost of revenue	274,298	492,238	494,911	506,281
Depreciation	12,859	21,020	21,262	20,238
Gross profit	117,004	187,712	203,008	184,733
Selling, general and administrative expenses	91,058	153,025	141,229	143,978
Impairment charges	0	15,810	0	0
Research and engineering	1,577	2,272	2,523	2,521
Depreciation and amortization	6,340	10,363	11,212	13,048
Acquisition-related expense (benefit), net	496	482	(1,453)	(5,167)
Litigation charges	0	1,600	6,320	0
Income from operations	17,533	4,160	43,177	30,353
Interest expense	2,052	4,386	4,762	4,622
(Loss) income before provision for income taxes	15,481	(226)	38,415	25,731
Provision for income taxes	5,870	1,942	13,765	9,740
Net (loss) income	9,611	(2,168)	24,650	15,991
Less: net income (loss) attributable to noncontrolling interests, net of taxes	43	7	(4)	(90)
Net (loss) income attributable to Mistras Group, Inc.	$ 9,568	$ (2,175)	$ 24,654	$ 16,081
(Loss) earnings per common share
Basic (in dollars per share)	$ 0.33	$ (0.08)	$ 0.85	$ 0.56
Diluted (in dollars per share)	$ 0.32	$ (0.08)	$ 0.82	$ 0.54
Weighted average common shares outstanding:
Basic (in shares)	28,989	28,422	28,856	28,613
Diluted (in shares)	30,125	28,422	29,891	29,590

Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	7 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2017	May 31, 2016	May 31, 2015
Statement of Comprehensive Income [Abstract]
Net (loss) income	$ 9,611	$ (2,168)	$ 24,650	$ 15,991
Other comprehensive income (loss):
Foreign currency translation adjustments	(9,625)	12,919	1,014	(19,602)
Comprehensive income (loss)	(14)	10,751	25,664	(3,611)
Less: net income (loss) attributable to noncontrolling interests	43	7	(4)	(90)
Foreign currency translation adjustments attributable to noncontrolling interests	6	4	1	5
Comprehensive income (loss) attributable to Mistras Group, Inc.	$ (51)	$ 10,748	$ 25,669	$ (3,516)

Consolidated Statements of Equity - USD ($) shares in Thousands, $ in Thousands	Total	Total Mistras Group, Inc. Stockholders’ Equity	Common Stock	Treasury Stock	Additional paid-in capital	Retained earnings	Accumulated other comprehensive income (loss)	Noncontrolling Interest
Balance (in shares) at May. 31, 2014			28,456	0
Balance at May. 31, 2014	$ 242,392	$ 242,104	$ 284	$ 0	$ 201,831	$ 41,500	$ (1,511)	$ 288
Increase (Decrease) in Stockholders' Equity
Net (loss) income	15,991	16,081				16,081		(90)
Other comprehensive income (loss), net of tax	(19,607)	(19,602)					(19,602)	(5)
Share-based payments (in shares)			21
Share-based payments	6,579	6,579			6,579
Net settlement on vesting of restricted stock units (in shares)			161
Net settlement on vesting of restricted stock units	(1,481)	(1,481)	$ 2		(1,483)
Excess tax benefit from share-based payment compensation	$ 388	388			388
Exercise of stock options (in shares)	65		65
Exercise of stock options	$ 750	750	$ 1		749
Balance (in shares) at May. 31, 2015			28,703	0
Balance at May. 31, 2015	245,012	244,819	$ 287	$ 0	208,064	57,581	(21,113)	193
Increase (Decrease) in Stockholders' Equity
Net (loss) income	24,650	24,654				24,654		(4)
Other comprehensive income (loss), net of tax	950	1,014					1,014	(64)
Share-based payments	6,394	6,394			6,394
Net settlement on vesting of restricted stock units (in shares)			182
Net settlement on vesting of restricted stock units	(1,091)	(1,091)	$ 2		(1,093)
Excess tax benefit from share-based payment compensation	$ (170)	(170)			(170)
Exercise of stock options (in shares)	55		55
Exercise of stock options	$ 543	543	$ 1		542
Balance (in shares) at May. 31, 2016			28,940	0
Balance at May. 31, 2016	276,288	276,163	$ 290	$ 0	213,737	82,235	(20,099)	125
Increase (Decrease) in Stockholders' Equity
Net (loss) income	9,611	9,568				9,568		43
Other comprehensive income (loss), net of tax	(9,631)	(9,625)					(9,625)	(6)
Share-based payments	4,627	4,627			4,627
Net settlement on vesting of restricted stock units (in shares)			212
Net settlement on vesting of restricted stock units	(2,323)	(2,323)	$ 2		(2,325)
Excess tax benefit from share-based payment compensation	568	568			568
Purchase of treasury stock (in shares)				(420)
Purchase of treasury stock	$ (9,000)	(9,000)		$ (9,000)
Exercise of stock options (in shares)	65		65
Exercise of stock options	$ 604	604			604
Balance (in shares) at Dec. 31, 2016			29,217	420
Balance at Dec. 31, 2016	270,744	270,582	$ (292)	$ 9,000	217,211	91,803	(29,724)	162
Increase (Decrease) in Stockholders' Equity
Net (loss) income	(2,168)	(2,175)				(2,175)		7
Other comprehensive income (loss), net of tax	12,923	12,919					12,919	4
Share-based payments	6,588	6,588			6,588
Net settlement on vesting of restricted stock units (in shares)			187
Net settlement on vesting of restricted stock units	(1,647)	(1,647)	$ 2		(1,649)
Retirement of treasury stock (in shares)			(1,146)	1,146
Retirement of treasury stock	0		$ (12)	$ 24,923		(24,911)
Purchase of treasury stock (in shares)				(726)
Purchase of treasury stock	$ (15,923)	(15,923)		$ (15,923)
Exercise of stock options (in shares)	37		37
Exercise of stock options	$ 275	275			275
Balance (in shares) at Dec. 31, 2017			28,295	0
Balance at Dec. 31, 2017	$ 270,792	$ 270,619	$ 282	$ 0	$ 222,425	$ 64,717	$ (16,805)	$ 173

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	7 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2017	May 31, 2016	May 31, 2015
Cash flows from operating activities
Net (loss) income	$ 9,611	$ (2,168)	$ 24,650	$ 15,991
Adjustments to reconcile net income to net cash provided by operating activities
Depreciation and amortization	19,199	31,383	32,474	33,286
Deferred income taxes	(174)	(4,854)	240	(1,745)
Share-based compensation expense	4,559	6,574	6,514	6,579
Impairment charges	0	15,810	0	0
Bad debt provision for unexpected customer bankruptcy	0	1,200	0	0
Charges associated with the exit of foreign operations	0	0	0	2,516
Fair value adjustments to contingent consideration	262	(463)	(2,066)	(5,382)
Other	559	79	(1,052)	1,647
Changes in operating assets and liabilities, net of effect of acquisitions
Accounts receivable	4,123	2,490	(4,999)	3,982
Inventories	628	(117)	1,595	388
Prepaid expenses and other current assets	(4,453)	(2,464)	(1,812)	(1,109)
Accounts payable	(3,667)	2,574	254	(6,571)
Accrued expenses and other liabilities	(2,301)	4,188	10,187	2,006
Income taxes payable	1,913	1,007	2,139	(1,748)
Net cash provided by operating activities	30,259	55,239	68,124	49,840
Cash flows from investing activities
Purchase of property, plant and equipment	(9,093)	(19,314)	(14,864)	(15,104)
Purchase of intangible assets	(697)	(1,255)	(1,315)	(866)
Acquisition of businesses, net of cash acquired	(8,262)	(83,424)	(1,743)	(34,677)
Proceeds from sale of equipment	678	1,196	1,170	996
Net cash used in investing activities	(17,374)	(102,797)	(16,752)	(49,651)
Cash flows from financing activities
Repayment of capital lease obligations	(4,490)	(6,492)	(7,870)	(8,653)
Proceeds from borrowings of long-term debt	386	6,653	2,737	2,232
Repayment of long-term debt	(11,919)	(2,101)	(17,580)	(11,457)
Proceeds from revolver	48,400	124,000	55,800	110,300
Repayments of revolver	(34,300)	(50,600)	(69,600)	(86,800)
Payment of contingent consideration for business acquisitions	(795)	(560)	(3,147)	(3,213)
Purchases of treasury stock	(9,000)	(15,923)	0	0
Taxes paid related to net share settlement of share-based awards	(2,323)	(1,647)	(1,091)	(1,481)
Excess tax benefit from share-based compensation	568	0	(170)	388
Proceeds from the exercise of stock options	604	275	543	750
Net cash provided by (used in) financing activities	(12,869)	53,605	(40,378)	2,066
Effect of exchange rate changes on cash and cash equivalents	(2,050)	2,340	(361)	(1,720)
Net change in cash and cash equivalents	(2,034)	8,387	10,633	535
Cash and cash equivalents:
Beginning of period	21,188	19,154	10,555	10,020
End of period	19,154	27,541	21,188	10,555
Supplemental disclosure of cash paid
Interest	2,079	4,264	4,151	4,504
Income taxes	8,119	3,063	10,686	13,243
Noncash investing and financing
Equipment acquired through capital lease obligations	1,829	3,185	8,248	8,031
Issuance of notes payable and other debt obligations primarily related to acquisitions	$ 325	$ 0	$ 0	$ 20,480

Description of Business and Basis of Presentation	12 Months Ended
Description of Business and Basis of Presentation	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of Business and Basis of Presentation	Description of Business and Basis of Presentation Description of Business Mistras Group, Inc. and subsidiaries (the Company) is a leading “one source” global provider of technology-enabled asset protection solutions used to evaluate the structural integrity and reliability of critical energy, industrial and public infrastructure. The Company combines industry-leading products and technologies, expertise in mechanical integrity (MI), non-destructive testing (NDT) and mechanical services and proprietary data analysis software to deliver a comprehensive portfolio of customized solutions, ranging from routine inspections to complex, plant-wide asset integrity assessments and management. These mission critical solutions enhance customers’ ability to extend the useful life of their assets, increase productivity, minimize repair costs, comply with governmental safety and environmental regulations, manage risk and avoid catastrophic disasters. The Company serves a global customer base of companies with asset-intensive infrastructure, including companies in the oil and gas, commercial aerospace and defense, fossil and nuclear power, alternative and renewable energy, public infrastructure, chemicals, transportation, primary metals and metalworking, pharmaceutical/biotechnology and food processing industries and research and engineering institutions. Principles of Consolidation The accompanying audited consolidated financial statements include the accounts of Mistras Group, Inc. and its wholly and majority-owned subsidiaries. For subsidiaries in which the Company’s ownership interest is less than 100%, the non-controlling interests are reported in stockholders’ equity in the accompanying consolidated balance sheets. The non-controlling interests in net income, net of tax, is classified separately in the accompanying consolidated statements of income. On January 3, 2017, the Company's Board of Directors approved a change in the Company's fiscal year from May 31 to December 31, effective December 31, 2016. In connection with this change, we previously filed a Transition Report on Form 10-K to report the results of the seven-month transition period from June 1, 2016 to December 31, 2016. In this Annual Report, the periods presented are the year ended December 31, 2017, the seven-month transition period from June 1, 2016 to December 31, 2016 and the years ended May 31, 2016 and 2015. The Company has also included unaudited data for the year ended December 31, 2016 and for the seven months ended December 31, 2015 (See Note 21). All significant intercompany accounts and transactions have been eliminated in consolidation. For fiscal 2016 and 2015, Mistras Group, Inc.’s and its subsidiaries’ fiscal years ended on May 31 except for the subsidiaries in the International segment, which ended on April 30. Accordingly, the Company’s International segment subsidiaries were consolidated on a one-month lag. Therefore, in the quarter and year of acquisition, results of acquired subsidiaries in the International segment were generally included in consolidated results for one less month than the actual number of months from the acquisition date to the end of the reporting period. As discussed in Note 7 - Acquisitions and Dispositions, during the lag period in fiscal 2015, the Company sold an international subsidiary, and decided to sell two additional international subsidiaries. Effective December 31, 2016, the Company's International segment is no longer consolidated on a one month lag, and such change for the seven month transition period ended December 31, 2016 was not material. Reclassifications Certain amounts in prior periods have been reclassified to conform to the current year presentation. Such reclassifications did not have a material effect on the Company's financial condition or results of operations as previously reported.

Summary of Significant Accounting Policies	12 Months Ended
Summary of Significant Accounting Policies	Dec. 31, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Revenue Recognition Revenue is generally recognized when persuasive evidence of an arrangement exists, services have been rendered or products have been delivered, the fee is fixed or determinable, and collectability is reasonably assured. Shipping and handling costs are included in cost of revenues. Taxes collected from customers and remitted to governmental authorities are presented in the consolidated statements of income on a net basis. One customer accounted for 11% and 12% of our revenues for the year ended December 31, 2017 and the transition period ended December 31, 2016, which primarily were generated from the Services segment. One customer accounted for 10% of our revenues in fiscal 2016, which primarily were generated from the Services segment. No customer accounted for 10% or more of our revenues in fiscal 2015. The following revenue recognition policies define the manner in which we account for specific transaction types: Services Most of our projects are short-term in nature and revenue is primarily derived from providing services on a time and material basis. Service arrangements generally consist of inspection professionals working under contract for a fixed period of time or on a specific customer project. Revenue is generally recognized when the service is performed in accordance with terms of each customer arrangement, upon completion of the earnings process and when collection is reasonably assured. At the end of any reporting period, earned revenue is accrued for services that have been provided which have not yet been billed. Reimbursable costs, including those related to travel and out-of-pocket expenses, are included in revenue, and equivalent amounts of reimbursable costs are included in cost of services. Products and Systems Sales of products and systems are recorded when the sales price is fixed and determinable and the risks and rewards of ownership are transferred (generally upon shipment) and when collectability is reasonably assured. These arrangements occasionally contain multiple elements or deliverables, such as hardware, software (that is essential to the functionality of the hardware) and related services. The Company recognizes revenue for delivered elements as separate units of accounting, when the delivered elements have standalone value, uncertainties regarding customer acceptance are resolved and there are no refund or return rights for the delivered elements. The Company establishes the selling prices for each deliverable based on vendor-specific objective evidence (“VSOE”), if available, third-party evidence, if VSOE is not available, or estimated selling price (“ESP”) if neither VSOE nor third-party evidence is available. The Company establishes VSOE of selling price using the price charged for a deliverable when sold separately and, in rare instances, using the price established by management having the relevant authority. Third-party evidence of selling price is established by evaluating largely similar and interchangeable competitor products or services in standalone sales to similarly situated customers. The Company determines ESP, by considering internal factors such as margin objectives, pricing practices and controls, customer segment pricing strategies and the product life cycle. Consideration is also given to market conditions such as competitor pricing strategies and industry technology life cycles. When determining ESP, the Company applies management judgment to establish margin objectives and pricing strategies and to evaluate market conditions and product life cycles. Changes in the aforementioned factors may result in a different allocation of revenue to the deliverables in multiple element arrangements and therefore may change the pattern and timing of revenue recognition for these elements, but will not change the total revenue recognized for the arrangement. A portion of the Company’s revenue is generated from engineering and manufacturing of custom products under long-term contracts that may last from several months to several years, depending on the contract. Revenues from long-term contracts are recognized on the percentage-of-completion method of accounting. Under the percentage-of-completion method of accounting revenues are recognized as work is performed. The percentage of completion at any point in time is generally based on total costs or total labor dollars incurred to date in relation to the total estimated costs or total labor dollars estimated at completion. The percentage of completion is then applied to the total contract revenue to determine the amount of revenue to be recognized in the period. Application of the percentage-of-completion method of accounting requires the use of estimates of costs to be incurred for the performance of the contract. Contract costs include all direct materials, direct labor costs and those indirect costs related to contract performance, such as indirect labor, supplies, tools, repairs, and all costs associated with operation of equipment. The cost estimation process is based upon the professional knowledge and experience of our engineers, project managers and financial professionals. Factors that are considered in estimating the work to be completed include the availability and productivity of labor, the nature and complexity of the work to be performed, the effect of change orders, the availability of materials, the effect of any delays in our project performance and the recoverability of any claims. Whenever revisions of estimated contract costs and contract values indicate that the contract costs will exceed estimated revenues, thus creating a loss, a provision for the total estimated loss is recorded in that period. Use of Estimates The preparation of financial statements in accordance with generally accepted accounting principles requires that the Company make estimates and assumptions that affect the reported amounts of assets, liabilities, revenue and expenses and disclosure of contingent assets and liabilities at the date of financial statements. The Company bases its estimates and assumptions on historical experience, known or expected trends and various other assumptions that it believes to be reasonable. As future events and their effects cannot be determined with precision, actual results could differ significantly from these estimates, which may cause the Company’s future results to be significantly affected. Cash and Cash Equivalents The Company considers all highly liquid investments purchased with an original maturity of three months or less to be cash equivalents. Accounts Receivable Accounts receivable are stated net of an allowance for doubtful accounts and sales allowances. Outstanding accounts receivable balances are reviewed periodically, and allowances are provided at such time that management believes it is probable that such balances will not be collected within a reasonable period of time. The Company extends credit to its customers based upon credit evaluations in the normal course of business, primarily with 30-day terms. Bad debts are provided for based on historical experience and management’s evaluation of outstanding accounts receivable. Accounts are written off when they are deemed uncollectible. One customer accounted for 7% and 11% of our accounts receivable as of December 31, 2017 and December 31, 2016, respectively. Inventories Inventories are stated at the lower of cost, as determined by using the first-in, first-out method, or market. Work in process and finished goods inventory include material, direct labor, variable costs and overhead. Purchased and Internal-Use Software The Company capitalizes certain costs that are incurred to purchase or to create and implement internal-use software, which includes software coding, installation and testing. Capitalized costs are amortized on a straight-line basis over three years, the estimated useful life of the software. Property, Plant and Equipment Property, plant and equipment are recorded at cost. Depreciation of property, plant and equipment is computed utilizing the straight-line method over the estimated useful lives of the assets. Amortization of leasehold improvements is computed utilizing the straight-line method over the shorter of the remaining lease term or estimated useful life. Repairs and maintenance costs are expensed as incurred. Goodwill Goodwill represents the excess purchase price of acquired businesses over the fair values attributed to underlying net tangible assets and identifiable intangible assets. We test goodwill for impairment at a “reporting unit” level (which for the Company is represented by (i) our Services segment, (ii) our Products and Systems segment, and (iii) the European component and (iv) Brazilian component of our International segment). Our annual impairment test is conducted on the first day of our fourth quarter. In connection with the change in our fiscal year to December 31, our annual test date is October 1. For the transition period ended December 31, 2016, a December 1 date was used and historically, prior to the fiscal year end change, the Company tested for impairment annually as of March 1. Goodwill is also tested for impairment whenever an event occurs or circumstances change that would more likely than not reduce the fair value of a reporting unit below its carrying amount. During the third quarter of 2017, there was a triggering event in the Products and Systems segment that resulted in a $13.2 million goodwill impairment charge. See Note 8 for further details. If the fair value of a reporting unit is less than its carrying value, this is an indicator that the goodwill assigned to that reporting unit may be impaired. As a result of the Company adopting ASU 2017-04, impairment will be recorded in the amount that fair value is less than carrying value, as the ASU eliminated step two of goodwill impairment process. The Company considers the income and market approaches to estimating the fair value of our reporting units, which requires significant judgment in evaluation of economic and industry trends, estimated future cash flows, discount rates and other factors. Impairment of Long-lived Assets The Company reviews the recoverability of its long-lived assets (or asset groups) on a periodic basis in order to identify indicators of a possible impairment. The assessment for potential impairment is based primarily on the Company’s ability to recover the carrying value of its long-lived assets from expected future undiscounted cash flows. If the total expected future undiscounted cash flows are less than the carrying amount of the assets, a loss is recognized for the difference between fair value (computed based upon the expected future discounted cash flows) and the carrying value of the assets. During the third quarter of 2017, there was a triggering event in the Products and Systems segment that resulted in a $2.6 million impairment charge of long-lived assets. See Note 9 for further details. Research and Engineering Research and product development costs are expensed as incurred. Advertising, Promotions and Marketing The costs for advertising, promotion and marketing programs are expensed as incurred and are included in selling, general and administrative expenses. Advertising expense was approximately $1.9 million, $1.2 million, $1.8 million and $2.2 million for the year ended December 31, 2017, the transition period ended December 31, 2016 and fiscal 2016 and 2015, respectively. Fair Value of Financial Instruments The carrying amounts of cash and cash equivalents, accounts receivable, accounts payable and other financial current assets and liabilities approximate fair value based on the short-term nature of the items. The carrying value of long-term debt approximates fair value due to the variable-rate structure of the debt. The fair value of the Company’s notes payable and capital lease obligations approximate their carrying amounts as those obligations bear interest at rates which management believes would currently be available to the Company for similar obligations. Foreign Currency Translation The financial position and results of operations of the Company’s foreign subsidiaries are measured using their functional currencies, which are their local currencies. Assets and liabilities of foreign subsidiaries are translated into the U.S. Dollar at the exchange rates in effect at the balance sheet date. Income and expenses are translated at the average exchange rate during the period. Translation gains and losses are reported as a component of other comprehensive (loss) income for the period and included in accumulated other comprehensive (loss) income within stockholders’ equity. Foreign currency (gains) and losses arising from transactions denominated in currencies other than the functional currency are included in net income, reported in SG&A expenses, and were approximately $0.6 million, $(0.7) million, $(0.1) million and $1.5 million for the year ended December 31, 2017, transition period ended December 31, 2016 and fiscal 2016 and 2015, respectively. Concentrations of Credit Risk Financial instruments that potentially subject the Company to concentrations of credit risk consist principally of cash and cash equivalents and accounts receivable. At times, cash deposits may exceed the limits insured by the Federal Deposit Insurance Corporation. The Company believes it is not exposed to any significant credit risk or risk of nonperformance of financial institutions. Self-Insurance The Company is self-insured for certain losses relating to workers’ compensation and health benefits claims. The Company maintains third-party excess insurance coverage for all workers' compensation and health benefit claims in excess of approximately $0.3 million per occurence to reduce its exposure from such claims. Self-insured losses are accrued when it is probable that an uninsured claim has been incurred but not reported and the amount of the loss can be reasonably estimated at the balance sheet date. Share-based Compensation The value of services received from employees and directors in exchange for an award of an equity instrument is measured based on the grant-date fair value of the award. Such value is recognized as a non-cash expense on a straight-line basis over the period the individual provides services, which is typically the vesting period of the award with the exception of awards with graded vesting that contain an internal performance measure where each tranche is recognized on a straight-line basis over its vesting period subject to the probability of meeting the performance requirements and adjusted for the number of shares expected to be earned. As share-based compensation expense is based on awards ultimately expected to vest, the amount of expense has been reduced for estimated forfeitures. The cost of these awards is recorded in selling, general and administrative expense in the Company’s consolidated statements of income. Income Taxes Income taxes are accounted for under the asset and liability method. Deferred income tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases and tax credit carry-forwards. Deferred income tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred income tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date. A valuation allowance is provided if it is more likely than not that some or all of a deferred income tax asset will not be realized. Financial accounting standards prescribe a minimum recognition threshold a tax position is required to meet before being recognized in the financial statements. These standards also provide guidance on de-recognition, measurement, and classification of amounts relating to uncertain tax positions, accounting for and disclosure of interest and penalties, accounting in interim periods and disclosures required. Interest and penalties related to unrecognized tax positions are recognized as incurred within “provision for income taxes” in the consolidated statements of income. Recent Accounting Pronouncements In August 2015, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") 2015-14, Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date, which defers the effective date of ASU 2014-09 for all entities by one year. This update is effective for public business entities for annual reporting periods beginning after December 15, 2017, including interim periods within those reporting periods. Earlier application is permitted only as of annual reporting periods beginning after December 15, 2016, including interim reporting periods within that reporting period. ASU 2014-09 will become effective for the Company beginning 2018. The ASU permits two methods of adoption: retrospectively to each prior reporting period presented (full retrospective method), or retrospectively with the cumulative effect of initially applying the guidance recognized at the date of initial application (the cumulative catch-up transition method). The ASU also requires expanded disclosures relating to the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. Additionally, qualitative and quantitative disclosures are required about customer contracts, significant judgments and changes in judgments, and assets recognized from the costs to obtain or fulfill a contract. The Company adopted ASU 2014-09 along with the related additional ASU’s on Topic 606 on January 1, 2018, utilizing the cumulative catch-up method. The result of adoption is immaterial to the Company's consolidated financial statements, largely because most of our projects are short-term in nature and billed on a time and material basis. The Company utilizes a practical expedient that provides for revenue to be recognize in an amount that corresponds directly with the value to the customer of the entity’s performance completed to date. The Company will make the additional required disclosures under Topic 606, starting with the Company's condensed consolidated financial statements in the first quarter of 2018. In November 2015, the FASB issued ASU No. 2015-17, Income Taxes (Topic 740): Balance Sheet Classification of Deferred Taxes. This amendment will simplify the presentation of deferred tax assets and liabilities on the balance sheet and require all deferred tax assets and liabilities to be treated as non-current. ASU 2015-17 is effective for fiscal years, and interim periods within those fiscal years beginning after December 15, 2016, with early adoption permitted. The Company adopted this guidance prospectively beginning in the first quarter of 2017, which did not have a material impact on the consolidated financial statements and related disclosures. In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842). This amendment supersedes previous accounting guidance (Topic 840) and requires all leases, with the exception of leases with a term of 12 months or less, to be recorded on the balance sheet as lease assets and lease liabilities. ASU 2016-02 is effective for fiscal years, and interim periods within those fiscal years beginning after December 15, 2018, with early adoption permitted. The standard requires lessees and lessors to recognize and measure leases at the beginning of the earliest period presented using a modified retrospective approach. The Company is evaluating the effect that ASU 2016-02 will have on its consolidated financial statements and related disclosures. In March 2016, the FASB issued ASU No. 2016-09, Stock Compensation (Topic 718). This amendment simplifies certain aspects of accounting for share-based payment transactions, which include accounting for income taxes and the related impact on the statement of cash flows, an option to account for forfeitures when they occur in addition to the existing guidance to estimate the forfeitures of awards, classification of awards as either equity or liabilities and classification on the statement of cash flows for employee taxes paid to tax authorities on shares withheld for vesting. ASU 2016-09 is effective for fiscal years, and interim periods within those fiscal years beginning after December 15, 2016, with early adoption permitted. The Company adopted this guidance prospectively beginning in the first quarter of 2017, and accordingly, is recording excess tax benefits and tax deficiencies as a component of income tax expense. In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (Topic 230). This amendment will provide guidance on the presentation and classification of specific cash flow items to improve consistency within the statement of cash flows. ASU 2016-15 is effective for fiscal years, and interim periods within those fiscal years beginning after December 15, 2017, with early adoption permitted. The Company does not expect that ASU 2016-15 will have a material impact on its consolidated financial statements and related disclosures. In November 2016, the FASB issued ASU No. 2016-18, Statement of Cash Flows (Topic 230). This amendment will clarify the presentation of restricted cash on the statement of cash flows. Amounts generally described as restricted cash and restricted cash equivalents should be included with cash and cash equivalents when reconciling the beginning and ending cash balances on the statement of cash flows. ASU 2016-18 is effective for fiscal years, and interim periods within those fiscal years beginning after December 15, 2017, with early adoption permitted. The Company does not expect that ASU 2016-18 will have a material impact on its consolidated financial statements and related disclosures. In January 2017, the FASB issued ASU No. 2017-04, Intangibles-Goodwill and Other (Topic 350). This amendment eliminates Step Two of the goodwill impairment test. Under the amendments in this update, entities should perform the annual goodwill impairment test by comparing the carrying value of its reporting units to their fair value. An entity should record an impairment charge for the amount by which the carrying amount exceeds the reporting unit’s fair value. Tax deductibility of goodwill should be considered in evaluating any reporting unit's impairment loss to be taken. ASU 2017-04 is effective for fiscal years beginning after December 15, 2019, with early adoption permitted. The Company early adopted ASU 2017-04 in the third quarter of 2017 for its consolidated financial statements and related disclosures. See Notes 8 and 9 for information on the impairment of assets in the Products and Systems reporting unit during the three months ended September 30, 2017. In May 2017, the FASB issued ASU 2017-09, Compensation-Stock Compensation (Topic 718) Scope of Modification Accounting. This amendment provides guidance concerning which changes to the terms or conditions of a share-based payment require an entity to apply modification accounting. Certain changes to stock awards, notably administrative changes, do not require modification accounting. There are three specific criteria that need to be met in order to prove that modification accounting is not required. ASU 2017-09 is effective for fiscal years, and interim period within those fiscal years, beginning after December 15, 2017, with early adoption permitted. The Company does not expect that ASU 2017-09 will have a material impact on its consolidated financial statements and related disclosures. In December 2017, the SEC staff issued Staff Accounting Bulletin No. 118 (“SAB 118”), which provides guidance on accounting for the tax effects of the Tax Cuts and Jobs Act (the "Tax Act"). SAB 118 provides a measurement period that should not extend beyond one year from the Tax Act enactment date for companies to complete the accounting under ASC 740. In accordance with SAB 118, a company must reflect the income tax effects of those aspects of the Act for which the accounting under ASC 740 is complete. To the extent that a company’s accounting for certain income tax effects of the Tax Act is incomplete but it is able to determine a reasonable estimate, it must record a provisional estimate in the financial statements. If a company cannot determine a provisional estimate to be included in the financial statements, it should continue to apply ASC 740 on the basis of the provisions of the tax laws that were in effect immediately before the enactment of the Tax Act. The Company considers the accounting for the Tax Act to be provisional as of December 31, 2017. The Company will complete the accounting for the tax effects of all of the provisions of the Tax Act within the required measurement period not to extend beyond one year from the enactment date.

Earnings per Share

12 Months Ended

Dec. 31, 2017

Earnings Per Share [Abstract]

Earnings per Share

Basic earnings per share is computed by dividing net income attributable to common shareholders by the weighted average number of shares outstanding during the period. Diluted earnings per share is computed by dividing net income attributable to common shareholders by the sum of (1) the weighted average number of shares of common stock outstanding during the period, and (2) the dilutive effect of assumed conversion of equity awards using the treasury stock method. With respect to the number of weighted average shares outstanding (denominator), diluted shares reflects: (i) only the exercise of options to acquire common stock to the extent that the options’ exercise prices are less than the average market price of common shares during the period and (ii) the pro forma vesting of restricted stock units.

The following table sets forth the computations of basic and diluted earnings per share:



	For the year ended December 31,			For the transition period ended December 31,		For the year ended May 31,
	2017			2016		2016		2015
Basic (loss) earnings per share
Numerator:
Net (loss) income attributable to Mistras Group, Inc.	$	(2,175	)	$	9,568	$	24,654	$	16,081
Denominator
Weighted average common shares outstanding	28,422			28,989		28,856		28,613
Basic (loss) earnings per share	$	(0.08	)	$	0.33	$	0.85	$	0.56

Diluted earnings per share:
Numerator:
Net income attributable to Mistras Group, Inc.	$	(2,175	)	$	9,568	$	24,654	$	16,081
Denominator
Weighted average common shares outstanding	28,422			28,989		28,856		28,613
Dilutive effect of stock options outstanding	—			791		712		719
Dilutive effect of restricted stock units outstanding	—			345		323		258
	28,422			30,125		29,891		29,590
Diluted (loss) earnings per share	$	(0.08	)	$	0.32	$	0.82	$	0.54

The following potential common shares were excluded from the computation of diluted earnings per share, as the effect would have been anti-dilutive:



	For the year ended December 31,			For the transition period ended December 31,	For the year ended May 31,
	2017			2016	2016	2015
Potential common stock attributable to stock options outstanding	810	₍₁	₎	—	5	6
Potential common stock attributable to restricted stock units (RSUs) and performance stock units (PSUs) outstanding	353	₍₂	₎	2	24	1
Total	1,163			2	29	7

(1) - 805 shares related to stock options were excluded from the calculation of diluted EPS due to the net loss for the period.

(2) - 351 shares related to RSUs and PSUs were excluded from the calculation of diluted EPS due to the net loss for the period.

Accounts Receivable, net

12 Months Ended

Dec. 31, 2017

Receivables [Abstract]

Accounts Receivable, net

Accounts receivable consist of the following:



	December 31,			December 31,
	2017			2016
Trade accounts receivable	$	141,952		$	133,704
Allowance for doubtful accounts	(3,872		)	(2,852		)
Accounts receivable, net	$	138,080		$	130,852

The Company had $14.4 million and $16.8 million of unbilled revenues accrued as of December 31, 2017 and December 31, 2016, respectively. Unbilled revenues as of December 31, 2017 are expected to be billed in the first quarter of 2018.

- Definition

The entire disclosure for claims held for amounts due a entity, excluding financing receivables. Examples include, but are not limited to, trade accounts receivables, notes receivables, loans receivables. Includes disclosure for allowance for credit losses.

+ References + Details

Property, Plant and Equipment, net

12 Months Ended

Dec. 31, 2017

Property, Plant and Equipment [Abstract]

Property, Plant and Equipment, net

Property, plant and equipment consist of the following:



		December 31,			December 31,
	Useful Life	2017			2016
	(Years)
Land		$	2,414		$	1,714
Building and improvements	30-40	24,003			19,261
Office furniture and equipment	5-8	14,230			9,069
Machinery and equipment	5-7	191,721			169,928
		232,368			199,972
Accumulated depreciation and amortization		(145,225		)	(126,823		)
Property, plant and equipment, net		$	87,143		$	73,149

Depreciation expense was approximately $22.4 million, $14.0 million, $22.9 million and $22.2 million for the year ended December 31, 2017, the transition period ended December 31, 2016 and fiscal 2016 and 2015, respectively.

Acquisitions and Dispositions

12 Months Ended

Dec. 31, 2017

Business Combinations [Abstract]

Acquisitions and Dispositions

Acquisitions

During the year ended December 31, 2017, the Company completed three acquisitions, one that performs mechanical services at height, located in Canada, a company located in the U.S. that primarily performs chemical and specialty process services and a company in the U.S. that performs a wide variety of non-destructive testing services. Both U.S. companies primarily provide services to the aerospace industry.

In these acquisitions, the Company acquired 100% of the equity interests of the entity based in Canada and one of the entities based in the U.S. in exchange for aggregate consideration of $79.5 million in cash, contingent consideration up to $2.4 million to be earned based upon the acquired business achieving specific performance metrics over the initial three years of operations from the acquisition date and $0.2 million for working capital adjustments yet to be finalized. The Company acquired the assets of one of the U.S. based entities noted above in exchange for aggregate consideration of $4.5 million in cash and contingent consideration up to $3.5 million to be earned based upon the acquired business achieving specific performance metrics over the initial three years of operations from the acquisition date. The Company accounted for these transactions in accordance with the acquisition method of accounting for business combinations.

During the transition period ended December 31, 2016, the Company completed three acquisitions. The Company purchased three companies, two that provide NDT services, located in Canada and one that provides mechanical services, located in the U.S.

For the Canadian acquisitions, the Company acquired 100% of the common stock of both acquirees in exchange for aggregate consideration of $1.3 million in cash, $0.3 million of notes payable and contingent consideration up to $0.6 million to be earned based upon the acquired businesses achieving specific performance metrics over their initial three years of operations from their acquisition dates. For the U.S. acquisition, the Company acquired assets of the acquiree in exchange for aggregate consideration of $7.0 million in cash and contingent consideration up to $2.0 million to be earned based upon the acquired businesses achieving specific performance metrics over the initial three years of operations from its acquisition date. The Company accounted for these three transactions in accordance with the acquisition method of accounting for business combinations.

Assets and liabilities of the acquired businesses were included in the consolidated balance sheets as of December 31, 2017 based on their estimated fair value on the date of acquisition as determined in a purchase price allocation, using available information and making assumptions management believes are reasonable. The Company is still in the process of completing its valuation of the assets, both tangible and intangible, and liabilities acquired for two of the acquisitions completed during the year ended December 31, 2017. Goodwill of $41.7 million primarily relates to expected synergies and assembled workforce, of which $39.7 million is generally deductible for tax purposes. Other intangible assets, primarily related to customer relationships and covenants not to compete, were $31.7 million. The results of operations of each of the acquisitions completed during the year ended December 31, 2017 and the transition period ended December 31, 2016 are included in each respective operating segment’s results of operations from the date of acquisition. The following table summarizes the estimated fair value of the assets acquired and liabilities assumed, the Company's allocation of purchase price and any subsequent adjustments made during the year ended December 31, 2017 and the transition period ended December 31, 2016:



	Year ended December 31, 2017			Transition Period
Number of entities	3			3

Cash paid	$	83,963		$	8,295
Working capital adjustments	150			—
Notes payable	—			325
Contingent consideration	3,407			1,630
Consideration paid	$	87,520		$	10,250

Current net assets	$	7,165		$	1,632
Debt and other long-term liabilities	(2,848		)	(214		)
Property, plant and equipment	11,115			953
Deferred tax asset (liability)	(1,278		)	392
Intangibles	31,671			3,367
Goodwill	41,695			4,120
Net assets acquired	$	87,520		$	10,250

The amortization period for intangible assets acquired ranges from two to fourteen years. The Company recorded $41.7 million and $4.1 million of goodwill in connection with its acquisitions for the year ended December 31, 2017 and the transition period ended December 31, 2016, respectively, reflecting the strategic fit and revenue and earnings growth potential of these businesses.

Revenue included in the consolidated statement of income for the year ended December 31, 2017 from the three businesses acquired in 2017 for the period subsequent to the closing of the transactions was approximately $17.9 million. Aggregate income from operations included in the consolidated statement of income for the year ended December 31, 2017 from the acquisitions for the period subsequent to the closing of each transaction was $0.8 million, inclusive of $0.9 million of acquisition-related expense. As these acquisitions were immaterial on an individual basis and in the aggregate, no unaudited pro forma financial information has been included in this report.

Dispositions

On May 22, 2015, the Company completed the sale of one of its Russian subsidiaries and recognized a loss of $0.4 million. On July 31, 2015, the Company completed the sale of its other subsidiary in Russia, as well as its subsidiary in Japan. For the year ended May 31, 2015, the Company recognized impairment charges of $2.1 million related to these sales. Aggregate charges associated with the exit of these three foreign operations was approximately $2.5 million and is included within selling, general and administrative expenses on the consolidated income statement for the year ended May 31, 2015. In the aggregate, the assets and liabilities of these subsidiaries represent 0.6% and 0.3% of consolidated assets and liabilities, respectively, and are included in their natural classifications on the consolidated balance sheet as of May 31, 2015.

During the fourth quarter of 2017, the Company began the process of marketing one of its subsidiaries in the Products and Systems segment for sale. The Company determined that the classification of being held for sale has been met as of December 31, 2017. For the year ended December 31, 2017, this subsidiary represented 0.6% of consolidated revenues and loss from operations was $3.5 million, inclusive of a $2.6 million impairment charge for long-lived assets (See Note 9). In the aggregate, the assets and liabilities of this subsidiary represents 0.4% and 0.2% of consolidated assets and liabilities, respectively, and are included in their natural classifications on the consolidated balance sheet as of December 31, 2017.

Acquisition-Related expense

In the course of its acquisition activities, the Company incurs costs in connection with due diligence, professional fees, and other expenses. Additionally, the Company adjusts the fair value of acquisition-related contingent consideration liabilities on a quarterly basis. These amounts are recorded as acquisition-related (benefit) expense, net, on the consolidated statements of income and were as follows for the year ended December 31, 2017, the transition period ended December 31, 2016 and fiscal 2016 and 2015:



	For the year ended December 31,			For the Transition Period ended December 31,		For the year ended May 31,
	2017			2016		2016			2015
Due diligence, professional fees and other transaction costs	$	945		$	231	$	629		$	215
Adjustments to fair value of contingent consideration liabilities	$	(463	)	$	265	$	(2,082	)	$	(5,382	)
Acquisition-related (benefit) expense, net	$	482		$	496	$	(1,453	)	$	(5,167	)

The Company’s contingent consideration liabilities are recorded on the balance sheet in accrued expenses and other liabilities.

Goodwill

12 Months Ended

Dec. 31, 2017

Goodwill and Intangible Assets Disclosure [Abstract]

Goodwill

The changes in the carrying amount of goodwill by segment is shown below:



	Services			International			Products and Systems			Total
Balance at May 31, 2016	$	119,683		$	36,340		$	13,197		$	169,220
Goodwill acquired during the year	4,120			—			—			4,120
Adjustments to preliminary purchase price allocations	(19		)	—			—			(19		)
Foreign currency translation	(392		)	(2,989		)	—			(3,381		)
Balance at December 31, 2016	$	123,392		$	33,351		$	13,197		$	169,940
Goodwill acquired during the year	41,695			—			—			41,695
Impairment charge	—			—			(13,197		)	(13,197		)
Adjustments to preliminary purchase price allocations	(211		)	—			—			(211		)
Foreign currency translation	925			4,286			—			5,211
Balance at December 31, 2017	$	165,801		$	37,637		$	—		$	203,438

During the second quarter of 2017, there were pending Products and Systems contract bids which management assessed as having a reasonable chance of success. During the third quarter of 2017, these contract bids were not awarded to the Company. As a result of this missed opportunity, the annual forecasting process was accelerated, resulting in lower expected future operating profits and cash flows. As such, during the third quarter of 2017, there were indicators that the carrying amount of the goodwill for the Products and Systems reporting unit may not have been recoverable due to the decline in the projected future cash flows.

The Company performed an analysis to determine any impairment of goodwill as well as long-lived assets (see Note 9). For the goodwill analysis, we used income and market approaches to estimate the fair value of the reporting unit, which required significant judgment in evaluation of economic and industry trends, estimated future cash flows, discount rates and other factors, and compared that fair value to the carrying value, and determined that the fair value of the reporting unit was less than the carrying value. The Company recorded an impairment charge of $13.2 million, based on the difference between the fair value and the carrying value of the reporting unit, which resulted in an impairment of the entire amount of goodwill for the Products and Systems reporting unit.

The Company performed an impairment test of its remaining reporting units as of October 1, 2017 and concluded that there was no impairment. For the year ended December 31, 2017, the Company reviewed goodwill for impairment on a reporting unit basis. As of December 31, 2017, the Company did not identify any changes in circumstances that would indicate the remaining carrying value of goodwill may not be recoverable.

The Company's cumulative goodwill impairment for the periods ended December 31, 2017 was $23.1 million, of which $13.2 million related to the Products and Systems segment and $9.9 million related to the International segment. The Company's cumulative goodwill impairment as of December 31, 2016 was $9.9 million, all of which is within its International segment.

Intangible Assets

12 Months Ended

Dec. 31, 2017

Goodwill and Intangible Assets Disclosure [Abstract]

Intangible Assets

The gross carrying amount and accumulated amortization of intangible assets were as follows:



		December 31,										December 31,
		2017										2016
	Useful Life (Years)	Gross Amount		Accumulated Amortization			Impairment			Net Carrying Amount		Gross Amount		Accumulated Amortization			Net Carrying Amount
Customer relationships	5-14	$	113,299	$	(58,107	)	$	(170	)	$	55,022	$	81,559	$	(50,417	)	$	31,142
Software/Technology	3-15	19,523		(14,133		)	(2,411		)	2,979		18,128		(12,577		)	5,551
Covenants not to compete	2-5	12,510		(10,438		)	—			2,072		11,143		(9,647		)	1,496
Other	2-5	10,109		(6,411		)	(32		)	3,666		7,266		(5,448		)	1,818
Total		$	155,441	$	(89,089	)	$	(2,613	)	$	63,739	$	118,096	$	(78,089	)	$	40,007

Amortization expense for the year ended December 31, 2017, the transition period ended December 31, 2016 and the years ended May 31, 2016 and 2015 was approximately $9.0 million, $5.2 million, $9.6 million and $11.1 million, respectively, including amortization of software/technology for these periods of $0.7 million, $0.5 million, $1.0 million and $0.9 million, respectively.

As described in Note 8, the Company performed an analysis to determine whether there was any impairment of long-lived

assets for the Products and Systems reporting unit. We used income and market approaches to estimate the fair value of the

long-lived assets, which requires significant judgment in evaluation of the useful lives of the assets, economic and industry

trends, estimated future cash flows, discount rates, and other factors. The result of the analysis was an impairment of $2.4 million to software/technology, $0.2 million to customer relationships and less than $0.1 million to other intangibles, which are

included in the impairment charges line on the consolidated statements of income for the year ended December 31, 2017.

Amortization expense in each of the five years and thereafter subsequent to December 31, 2017 related to the Company’s intangible assets is expected to be as follows:



	Expected Amortization Expense

2018	$	10,117
2019	8,952
2020	7,483
2021	6,411
2022	6,076
Thereafter	24,700
Total	$	63,739

Long-Term Debt

12 Months Ended

Dec. 31, 2017

Debt Disclosure [Abstract]

Long-Term Debt

Long-term debt consists of the following:



	December 31,
	2017			2016
Senior credit facility	$	156,948		$	82,776
Notes payable	228			320
Other	9,702			4,200
Total debt	166,878			87,296
Less: Current portion	(2,358		)	(1,379		)
Long-term debt, net of current portion	$	164,520		$	85,917

Senior Credit Facility

On December 8, 2017, the Company entered into a Fourth Amended and Restated Credit Agreement (“Credit Agreement”). The Credit Agreement increased the Company’s revolving line of credit from $175.0 million to $250.0 million and provides that under certain circumstances the line of credit can be increased to $300.0 million. The Company may continue to borrow up to $30.0 million in non-U.S. Dollar currencies and use up to $10.0 million of the credit limit for the issuance of letters of credit. The maturity date of the Credit Agreement is December 7, 2022. At December 31, 2017, the Company had borrowings of $156.9 million and letters of credit of $4.9 million were outstanding under the Credit Agreement. The Company has capitalized costs of $0.8 million associated with debt modifications.

Loans under the Credit Agreement bear interest at LIBOR plus an applicable LIBOR margin ranging from 1% to 2%, or a base rate less a margin of 1.25% to 0.375%, at the option of the Company, based upon the Company’s Funded Debt Leverage Ratio. Funded Debt Leverage Ratio is generally the ratio of (1) all outstanding indebtedness for borrowed money and other interest-bearing indebtedness as of the date of determination to (2) EBITDA (which is (a) net income, less (b) income (or plus loss) from discontinued operations and extraordinary items, plus (c) income tax expenses, plus (d) interest expense, plus (e) depreciation, depletion, and amortization (including non-cash loss on retirement of assets), plus (f) stock compensation expense, less (g) cash expense related to stock compensation, plus (h) certain amounts of EBITDA of acquired business for the prior twelve months, plus (i) certain expenses related to the closing of the Credit Agreement, plus (j) non-cash expenses which do not (in the current or any future period) represent a cash item (excluding non-cash gains which increase net income), plus (k) non-recurring charges (not to exceed $5 million in the four consecutive quarters immediately preceding the date of determination) for items such as severance, lease termination charges, asset write-offs and litigation settlements paid during the period, all determined for the period of four consecutive fiscal quarters immediately preceding the date of determination. The Company has the benefit of the lowest margin if its Funded Debt Leverage Ratio is equal to or less than 0.5 to 1, and the margin increases as the ratio increases, to the maximum margin if the ratio is greater than 2.75 to 1. The Company will also bear additional costs for market disruption, regulatory changes effecting the lenders’ funding costs, and default pricing of an additional 2% interest rate margin on any amounts not paid when due. Amounts borrowed under the Credit Agreement are secured by liens on substantially all of the assets of the Company and is guaranteed by some of our subsidiaries.

The Credit Agreement contains financial covenants requiring that the Company maintain a Funded Debt Leverage Ratio of no greater than 3.5 to 1 and an Interest Coverage Ratio of at least 3.0 to 1. Interest Coverage Ratio means the ratio, as of any date of determination, of (a) EBITDA for the 12 month period immediately preceding the date of determination, to (b) all interest, premium payments, debt discount, fees, charges and related expenses of the Company and its subsidiaries in connection with borrowed money (including capitalized interest) or in connection with the deferred purchase price of assets, in each case to the extent treated as interest in accordance with GAAP, paid during the 12 month period immediately preceding the date of determination. The Company can elect to increase the Funded Debt Leverage Ratio to 3.75 to 1 temporarily for four fiscal quarters immediately following the fiscal quarter in which the Company acquires another business. The Company can make this election twice during the term of the Credit Agreement.

The Credit Agreement also limits the Company’s ability to, among other things, create liens, make investments, incur more indebtedness, merge or consolidate, make dispositions of property, pay dividends and make distributions to stockholders or repurchase our stock, enter into a new line of business, enter into transactions with affiliates and enter into burdensome agreements. The Credit Agreement does not limit the Company’s ability to acquire other businesses or companies except that the acquired business or company must be in the Company's line of business, the Company must be in compliance with the financial covenants on a pro forma basis after taking into account the acquisition, and, if the acquired business is a separate subsidiary, in certain circumstances the lenders will receive the benefit of a guaranty of the subsidiary and liens on its assets and a pledge of its stock.

As of December 31, 2017, the Company was in compliance with the terms of the Credit Agreement, and has undertaken to continuously monitor compliance with these covenants.

Notes Payable and Other Debt

In connection with certain of its acquisitions, the Company issued subordinated notes payable to the sellers. The maturity of the notes that remain outstanding are three years from the date of acquisition and bear interest at the prime rate for the Bank of Canada, currently 3.2% as of December 31, 2017. Interest expense is recorded in the consolidated statements of income.

The Company's other debt includes local bank financing provided at the local subsidiary levels used to support working capital requirements and fund capital expenditures. At December 31, 2017, there was approximately $9.7 million outstanding, payable at various times from 2018 to 2029. Monthly payments range from $1 thousand to $18 thousand. Interest rates range from 0.6% to 6.2%.

The Company has evaluated current market conditions and borrower credit quality and has determined that the carrying value of its long-term debt approximates fair value. The fair value of the Company’s notes payable and capital lease obligations approximates their carrying amounts based on anticipated interest rates which management believes would currently be available to the Company for similar issues of debt.

Scheduled principal payments due under all borrowing agreements in each of the five years and thereafter subsequent to December 31, 2017 are as follows:



2018	$	2,358
2019	1,664
2020	1,243
2021	892
2022	157,728
Thereafter	2,993
Total	$	166,878

Fair Value Measurements

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

Fair Value Measurements

The Company performs fair value measurements in accordance with the guidance provided by ASC 820, Fair Value Measurements and Disclosures. ASC 820 defines fair value as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. It also establishes a three level hierarchy that prioritizes the inputs used to measure fair value. The three levels of the hierarchy are defined as follows:

Level 1 — Inputs are unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date.

Level 2 — Observable inputs other than quoted prices included in Level 1, including quoted prices for similar assets or liabilities in active markets, quoted prices for identical assets or liabilities in inactive markets, inputs other than quoted prices that are observable for the asset or liability and inputs derived principally from or corroborated by observable market data.

Level 3 — Unobservable inputs reflecting the Company’s own assumptions about inputs that market participants would use in pricing the asset or liability based on the best information available.

Financial instruments measured at fair value on a recurring basis

The fair value of contingent consideration liabilities was estimated using a discounted cash flow technique with significant

inputs that are not observable in the market and thus represents a Level 3 fair value measurement as defined in ASC 820. The

significant inputs in the Level 3 measurement not supported by market activity include the probability assessments of expected

future cash flows related to the acquisitions, appropriately discounted considering the uncertainties associated with the

obligation, and as calculated in accordance with the terms of the applicable acquisition agreements.

The following table represents the changes in the fair value of Level 3 contingent consideration:



Balance at May 31, 2016	$	2,075
Acquisitions	1,630
Payments	(795		)
Accretion of liability	136
Revaluation	126
Foreign currency translation	(78		)
Balance at December 31, 2016	$	3,094
Acquisitions	3,407
Payments	(560		)
Accretion of liability	272
Revaluation	(735		)
Foreign currency translation	30
Balance at December 31, 2017	$	5,508

Financial instruments not measured at fair value on a recurring basis

The Company has evaluated current market conditions and borrower credit quality and has determined that the carrying value

of its long-term debt approximates fair value. The fair value of the Company’s notes payable and capital lease obligations

approximates their carrying amounts based on anticipated interest rates which management believes would currently be

available to the Company for similar issuances of debt.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Share-Based Compensation

12 Months Ended

Dec. 31, 2017

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Share-Based Compensation

The Company has share-based incentive awards outstanding to its eligible employees and Directors under three employee stock ownership plans: (i) the 2007 Stock Option Plan (the 2007 Plan), (ii) the 2009 Long-Term Incentive Plan (the 2009 Plan) and (iii) the 2016 Long-Term Incentive Plan. No further awards may be granted under either the 2007 Plan or the 2009 Plan, although awards granted under the 2007 Plan and 2009 Plan remain outstanding in accordance with their terms. Awards granted under the 2016 Plan may be in the form of stock options, restricted stock units and other forms of share-based incentives, including performance restricted stock units, stock appreciation rights and deferred stock rights. The 2016 Plan allows for the grant of awards of up to approximately 1,700,000 shares of common stock, of which 1,438,000 shares were available for future grants as of December 31, 2017. As of December 31, 2017, there was an aggregate of approximately 2,130,000 stock options outstanding and approximately 724,000 unvested restricted stock units outstanding under the 2009 Plan and the 2007 Plan.

Stock Options

For the year ended December 31, 2017 and the transition period ended December 31, 2016, the Company did not have any share-based compensation expense related to stock option awards. For each of the fiscal years ended May 31, 2016 and 2015, the Company recognized share-based compensation expense related to stock option awards of less than $0.1 million. No stock options were granted during the year ended December 31, 2017, the transition period ended December 31, 2016 or the years ended May 31, 2016 and 2015. As of December 31, 2017, no unrecognized compensation costs remained related to stock option awards. Cash proceeds from, and the intrinsic value of stock options exercised during the year ended December 31, 2017, the transition period ended December 31, 2016 and the years ended May 31, 2016 and 2015 were as follows:



	For the year ended December 31,		For the Transition Period ended December 31,		For the year ended May 31,
	2017		2016		2016		2015
Cash proceeds from options exercised	$	275	$	604	$	543	$	750
Aggregate intrinsic value of options exercised	580		993		658		563

A summary of the stock option activity, weighted average exercise prices, and options outstanding and exercisable as of December 31, 2017, the transition period ended December 31, 2016 and the years ended May 31, 2016 and 2015 is as follows (in thousands, except per share amounts):



	For the year ended December 31,				For the Transition Period ended December 31,				For the year ended May 31,
	2017				2016				2016				2015
	Common Stock Options		Weighted Average Exercise Price		Common Stock Options		Weighted Average Exercise Price		Common Stock Options		Weighted Average Exercise Price		Common Stock Options		Weighted Average Exercise Price
Outstanding at beginning of year:	2,167		$	13.33	2,232		$	13.21	2,287		$	13.13	2,352		$	13.09
Granted	—		$	—	—		$	—	—		$	—	—		$	—
Exercised	(37	)	$	7.39	(65	)	$	9.27	(55	)	$	9.87	(65	)	$	11.54
Expired or forfeited	—		$	—	—		$	—	—		$	—	—		$	—
Outstanding at end of year:	2,130		$	13.43	2,167		$	13.33	2,232		$	13.21	2,287		$	13.13



			For the year ended December 31, 2017
			Options Outstanding			Options Exercisable
Range of Exercise Prices	Total Options Outstanding		Weighted Average Remaining Life (Years)	Weighted Average Exercise Price		Number Exercisable		Weighted Average Exercise Price
$10.00-$11.54	35		1.1	$	10.54	35		$	10.54
$13.46-$22.35	2,095		1.7	$	13.48	2,095		$	13.48
	2,130					2,130

Aggregate Intrinsic Value	$	21,374				$	21,374

Restricted Stock Unit Awards

The Company recognized approximately $4.5 million of share-based compensation for the year ended December 31, 2017, $2.6 million of share-based compensation for the transition period ended December 31, 2016, $4.4 million of share-based compensation in fiscal 2016 and $4.7 million of share-based compensation in fiscal 2015 related to restricted stock unit awards. As of December 31, 2017, there were approximately $8.2 million of unrecognized compensation costs, net of estimated forfeitures, related to restricted stock unit awards, which are expected to be recognized over a remaining weighted average period of 2.3 years. Approximately 185,000 restricted stock units vested in the year ended December 31, 2017, of which the fair value of these units was $3.4 million. Approximately 207,000 restricted stock units vested in the transition period ended December 31, 2016, of which the fair value of these units was $5.1 million. Approximately 223,000 restricted stock units vested in fiscal 2016 and 232,000 restricted stock units vested in fiscal 2015. The fair value of these units was $3.5 million and $5.2 million, respectively. Upon vesting, restricted stock units are generally net share-settled to cover the required minimum withholding tax and the remaining amount is converted into an equivalent number of shares of common stock.

During the year ended December 31, 2017, the Company granted approximately 21,000 shares of fully-vested common stock to its five non-employee directors, in connection with its non-employee director compensation plan, which shares had a grant date fair value of approximately $0.4 million. During the transition period ended December 31, 2016, the Company granted approximately 10,000 shares of fully-vested common stock to its five non-employee directors, in connection with its non-employee director compensation plan, which shares had a grant date fair value of approximately $0.3 million. During the years ended May 31, 2016 and 2015, the Company granted approximately 28,000 and 21,000 shares, respectively, of fully-vested common stock to its five non-employee directors, in connection with its non-employee director compensation plan. These shares had a grant date fair value of approximately $0.5 million and $0.4 million, respectively, which is included in the share-based compensation expense recorded during the years ended May 31, 2016 and 2015.



	For the year ended December 31,				For the transition period ended December 31,				For the year ended May 31,
	2017				2016				2016				2015
	Units		Weighted Average Grant-Date Fair Value		Units		Weighted Average Grant-Date Fair Value		Units		Weighted Average Grant-Date Fair Value		Units		Weighted Average Grant-Date Fair Value
Outstanding at beginning of period:	569		$	20.81	575		$	18.85	564		$	20.47	628		$	19.37
Granted	183		$	21.26	219		$	24.48	264		$	16.73	192		$	21.87
Released	(185	)	$	20.49	(207	)	$	19.40	(223	)	$	20.40	(232	)	$	18.17
Forfeited	(35	)	$	21.45	(18	)	$	19.55	(30	)	$	19.26	(24	)	$	20.57
Outstanding at end of period:	532		$	21.05	569		$	20.81	575		$	18.85	564		$	20.47

Performance Restricted Stock Units

The Company maintains Performance Restricted Stock Units (PRSUs) that have been granted to select executives and senior officers whose ultimate payout is based on the Company’s performance over a one-year period based on three metrics, as defined: (1) Operating Income, (2) Adjusted EBITDAS and (3) Revenue. There is a discretionary portion of the PRSUs based on individual performance, at the discretion of the Compensation Committee (Discretionary PRSUs). PRSUs and Discretionary PRSUs generally vest ratably on each of the first four anniversary dates upon completion of the performance period, for a total requisite service period of up to five years and have no dividend rights.

PRSUs are equity-classified and compensation costs are initially measured using the fair value of the underlying stock at the date of grant, assuming that the target performance conditions will be achieved. Cumulative compensation costs related to the PRSUs are subsequently adjusted for changes in the expected outcomes of the performance conditions.

Discretionary PRSUs are liability-classified and adjusted to fair value (with a corresponding adjustment to compensation expense) based upon the targeted number of shares to be awarded and the fair value of the underlying stock each reporting period until approved by the Compensation Committee, at which point they are classified as equity.

A summary of the Company's Performance Restricted Stock Unit activity is presented below:



	For the year ended December 31, 2017				For the Transition Period ended December 31, 2016
	Units		Weighted Average Grant-Date Fair Value		Units		Weighted Average Grant-Date Fair Value
Outstanding at beginning of period:	290		$	16.01	328		$	17.02
Granted	128		$	20.42	105		$	24.90
Performance condition adjustments, net	(68	)	$	20.55	(54	)	$	24.49
Released	(72	)	$	15.82	(89	)	$	24.50
Forfeited	—		$	—	—		$	—
Outstanding at end of period:	278		$	17.00	290		$	16.01

In fiscal 2014, the company granted one-year, two-year and three-year PRSUs to its executive and certain other senior officers. These units had requisite service periods of three years and have no dividend rights. The actual payout of these units, before the fiscal 2016 modification as described below, was based on the Company’s performance over one, two and three-year periods (based on pre-established targets) and a market condition modifier based on total shareholder return (TSR) compared to an industry peer group. The one-year and two-year performance conditions of the fiscal 2014 awards were evaluated before modification of the awards and not achieved. The one-year and two-year market conditions of the fiscal 2014 awards were evaluated before modification of the awards and achieved. Compensation costs related to the TSR conditions for the one-year and two-year 2014 awards described above were fixed at the measurement date, and not subsequently adjusted. The one-year and two-year awards related to market conditions were paid at 170% and 105%, respectively, of target, upon vesting during the transition period ended December 31, 2016. The three-year performance and market condition awards were surrendered as part of the fiscal 2016 modification described below.

In fiscal 2015, the company granted PRSUs to its executive and certain other senior officers. These units have requisite service periods of three years and have no dividend rights. The actual payout of these units, before the fiscal 2016 modification as described below, was based on the Company’s performance over the three-year period (based on pre-established targets) and a market condition modifier based on (TSR) compared to an industry peer group. The 2015 awards were surrendered as part of the fiscal 2016 modification described below.

In the first quarter of fiscal 2016, the Company modified its equity compensation program and granted 154,000 PRSUs to its executive and certain other senior officers. As a condition for receiving any awards under the revised fiscal 2016 plan, the executive and senior officers surrendered and released all rights to receive any shares under the three-year 2014 awards and three-year 2015 awards with a performance or market condition. The Company has accounted for the fiscal 2016 awards as modifications in accordance with ASC 718, Compensation - Stock Compensation. These units have requisite service periods of five years and have no dividend rights.

The fiscal 2016 PRSUs increased by approximately 104,000 units to a total of 258,000 units, which represents Company performance above target as well as individual performance, and was approved by the Compensation Committee in August 2016.

For the transition period ended December 31, 2016, 105,000 PRSUs were granted. There was a 73,000 unit reduction to these awards, which represents Company performance below target, during the transition period ended December 31, 2016. As of December 31, 2016, the aggregate liability related to 12,000 outstanding Discretionary PRSUs was less than $0.1 million and is classified within accrued expenses and other liabilities on the consolidated balance sheet. The Compensation Committee approved these PSUs in the first quarter of 2017, which reduced them by 3,000 units. The discretionary portion of these awards were reclassed from a liability to equity on the consolidated balance sheet upon Compensation Committee approval.

For the year ended December 31, 2017, 128,000 PRSUs were granted. There was a 65,000 unit reduction to these awards, which represents Company performance below target, during the year ended December 31, 2017. As of December 31, 2017, the aggregate liability related to 13,000 outstanding Discretionary PRSUs was less than $0.1 million and is classified within accrued expenses and other liabilities on the consolidated balance sheet.

Compensation expense related to all PRSUs described above was $1.7 million, $1.7 million, $1.6 million and $1.5 million for the year ended December 31, 2017, the transition period ended December 31, 2016 and the years ended May 31, 2016 and 2015, respectively. At December 31, 2017, there was $2.3 million of total unrecognized compensation costs related to approximately 278,000 nonvested performance restricted stock units. These costs are expected to be recognized over a weighted-average period of approximately 2.0 years.

For the year ended December 31, 2017, the transition period ended December 31, 2016 and the fiscal years ended May 31, 2016 and 2015, the income tax benefit recognized on all share based compensation arrangements referenced above was approximately $2.2 million, $1.6 million, $2.2 million and $2.3 million, respectively.

Income Taxes

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Income Taxes

Income before provision for income taxes is as follows:



	For the year ended December 31,			For the Transition Period ended December 31,		For the year ended May 31,
	2017			2016		2016		2015
(Loss) income before provision for income taxes from:
U.S. operations	$	(7,303	)	$	5,116	$	27,772	$	26,893
Foreign operations	7,077			10,365		10,643		(1,162		)
(Loss) Earnings before income taxes	$	(226	)	$	15,481	$	38,415	$	25,731

The provision for income taxes consists of the following:



	For the year ended December 31,			For the Transition Period ended December 31,			For the year ended May 31,
	2017			2016			2016			2015
Current
Federal	$	3,558		$	1,990		$	9,156		$	8,489
States and local	39			483			1,537			1,177
Foreign	3,131			3,569			3,672			1,493
Reserve for uncertain tax positions	71			(39		)	(529		)	(48		)
Total current	6,799			6,003			13,836			11,111
Deferred
Federal	(3,857		)	6			82			(145		)
States and local	(810		)	(28		)	(51		)	(126		)
Foreign	(437		)	(514		)	(557		)	(2,416		)
Total deferred	(5,104		)	(536		)	(526		)	(2,687		)
Net change in valuation allowance	247			403			455			1,316
Net deferred	(4,857		)	(133		)	(71		)	(1,371		)
Provision for income taxes	$	1,942		$	5,870		$	13,765		$	9,740

The provision for income taxes differs from the amount computed by applying the statutory federal tax rate to income tax as follows:



	For the year ended December 31,					For the Transition period ended December 31,
	2017					2016
Federal tax at statutory rate	$	(79	)	35.0	%	$	5,418		35.0	%
State taxes, net of federal benefit	(502		)	221.6	%	296			1.9	%
Foreign tax	217			(95.8	)%	(573		)	(3.7	)%
Contingent consideration	(63		)	27.7	%	(4		)	—	%
Permanent differences	377			(166.4	)%	373			2.4	%
Transition tax, net of foreign tax credits	3,942			(1,741.4	)%	—			—	%
Federal tax rate change due to the Tax Act	(1,956		)	864.0	%	—			—	%
Other	(241		)	106.5	%	(43		)	(0.3	)%
Change in valuation allowance	247			(109.1	)%	403			2.6	%
Total provision for income taxes	$	1,942		(857.9	)%	$	5,870		37.9	%

On December 22, 2017, the United States enacted fundamental changes to the federal tax law following the passage of the Tax Act.

The Tax Act is complex and significantly changes the U.S. corporate tax system by, among other things, (a) reducing the federal corporate tax rate from 35% to 21% for tax years beginning after December 31, 2017, (b) replacing the prior system of taxing corporations on foreign earnings of their foreign subsidiaries when the earnings are repatriated with a partial territorial tax system that provides a 100% dividends-received deduction (DRD) to domestic corporations for foreign-sourced dividends received from 10%-or-more owned foreign corporations, (c) subjecting certain unrepatriated foreign earnings to a mandatory one-time transition tax on post-1986 earnings and profits ("the transition tax"), and (d) further limiting a public entity's ability to deduct compensation in excess of $1 million for covered employees.

Our income tax expense for 2017 was $1.9 million. This amount reflects a net tax benefit of $2.3 million as a result of the Tax Act due to the remeasurement of federal deferred tax assets and liabilities from 35% to 21%. This amount also includes a charge of $3.9 million due to the transition tax. Additionally, we incurred a charge attributable to reducing our deferred tax assets by $0.3 million due to changes made to executive compensation rules pursuant to the Tax Act.



	For the year ended May 31,
	2016					2015
Federal tax at statutory rate	$	13,445		35.0	%	$	9,006		35.0	%
State taxes, net of federal benefit	966			2.5	%	683			2.7	%
Foreign tax	(610		)	(1.6	)%	(517		)	(2.0	)%
Contingent consideration	(425		)	(1.1	)%	(914		)	(3.6	)%
Permanent differences	245			0.6	%	196			0.8	%
Other	(311		)	(0.8	)%	(30		)	(0.1	)%
Change in valuation allowance	455			1.2	%	1,316			5.1	%
Total provision for income taxes	$	13,765		35.8	%	$	9,740		37.9	%

Deferred income tax attributes resulting from differences between financial accounting amounts and income tax basis of assets and liabilities are as follows:



	December 31,
	2017			2016
Deferred income tax assets
Allowance for doubtful accounts	$	838		$	969
Inventory	265			236
Intangible assets	2,255			2,529
Accrued expenses	2,560			5,157
Net operating loss carryforward	3,729			4,094
Capital lease obligations	1,004			1,140
Capital losses	463			719
Foreign tax credit carryover	618			—
Deferred share-based compensation	4,080			5,802
Other	484			285
Deferred income tax assets	16,296			20,931
Valuation allowance	(4,044		)	(3,896		)
Net deferred income tax assets	12,252			17,035
Deferred income tax liabilities
Property and equipment	(6,893		)	(8,655		)
Goodwill	(6,578		)	(13,586		)
Intangible assets	(5,972		)	(5,051		)
Other	(6		)	(11		)
Deferred income tax liabilities	(19,449		)	(27,303		)
Net deferred income taxes	$	(7,197	)	$	(10,268	)

As of December 31, 2017, the Company had federal net operating loss carry forwards (NOLs) in the amount of approximately $0.2 million which may be utilized subject to limitation under Internal Revenue Code section 382. The federal NOLs expire at various times from 2031 to 2033. In addition, as of December 31, 2017, the Company had state and foreign NOLs of $38.4 million and $11.0 million, respectively. The state NOLs expire at various times from 2020 to 2037. Approximately $0.7 million of the foreign NOLs expire at various times from 2022 to 2037, while the remainder of the Company's foreign NOLs do not expire.

In assessing the ability to realize deferred tax assets, management considers whether it is more likely than not that some portion or all of the deferred tax assets will be realized. Valuation allowances are provided when management believes the Company's deferred tax assets are not recoverable based on an assessment of estimated future taxable income that incorporates ongoing, prudent and feasible tax planning strategies. At December 31, 2017 and December 31, 2016, the Company has a valuation allowance of approximately $4.0 million and $3.9 million, respectively, primarily against certain state and foreign NOLs, capital losses generated by the disposals of certain foreign subsidiaries and other specific deferred tax assets. The increase of $0.1 million is primarily attributable to a $0.2 million increase in against state deferred tax assets and a net $0.1 million decrease in federal valuation allowance attributable to the Tax Act. Except for those deferred tax assets subject to the valuation allowance, management believes that it will realize all deferred tax assets as a result of sufficient future taxable income in each tax jurisdiction in which the Company has deferred tax assets.

The following table summarizes the changes in the Company’s gross unrecognized tax benefits, excluding interest and penalties:



	For the year ended December 31,			For the Transition Period ended December 31,
	2017			2016
Balance at beginning of period	$	267		$	303
Additions for tax positions related to the current fiscal period	11			8
Additions for tax positions related to prior years	188			—
Decreases for tax positions related to prior years	—			(11		)
Impact of foreign exchange fluctuation	10			—
Settlements	(198		)	—
Reductions related to the expiration of statutes of limitations	(122		)	(33		)
Balance at end of period	$	156		$	267

The Company has recorded the unrecognized tax benefits in other long-term liabilities in the consolidated balance sheets. As of December 31, 2017 and December 31, 2016, there were approximately $0.2 million and $0.3 million of unrecognized tax benefits, respectively, including penalties and interest that if recognized would favorably affect the effective tax rate. Interest and penalties related to unrecognized tax benefits are recorded in income tax expense and are not significant for the year ended December 31, 2017, the transition period ended December 31, 2016 and the fiscal years ended May 31, 2016 and 2015. The Company anticipates a decrease to its unrecognized tax benefits of less than $0.1 million excluding interest and penalties within the next 12 months.

The Company is subject to taxation in the United States and various states and foreign jurisdictions. The Company is no longer subject to U.S. federal income tax examinations for years ending before May 31, 2015 and generally is no longer subject to state, local or foreign income tax examinations by tax authorities for years ending before May 31, 2014.

Net income (loss) of foreign subsidiaries was $4.1 million, $6.9 million, $7.5 million and $(0.8) million for the year ended December 31, 2017, the transition period ended December 31, 2016, fiscal 2016 and 2015, respectively. Generally, it has been our practice and intention to reinvest the earnings of our non-U.S. subsidiaries in those operations. As previously noted, the Tax Act made significant changes to the taxation of undistributed earnings, requiring that all previously untaxed earnings and profits of our controlled foreign operations be subjected to the transition tax. Since these earnings have now been subjected to U.S. federal tax they would only be potentially subject to limited other taxes, including foreign withholding and certain state taxes. As of December 31, 2017, the Company has not recognized U.S. tax expense on its undistributed international earnings or losses of its foreign subsidiaries since it intends to indefinitely reinvest the earnings outside the United States.

The Company considers the accounting of the effects of the Tax Act to be estimates. The provisional amounts recorded are based on the Company’s current interpretation and understanding of the Tax Act and may change as the Company receives additional clarification and implementation guidance and finalizes their analysis of all impacts and positions with regard to the Tax Act. The Company will continue to gather and evaluate the data and guidance to refine the income tax impact of the Tax Act. The effect of the change in federal corporate tax rate from 35% to 21% is subject to change based on resolution of estimates used in determining the amounts of deferred tax assets and liabilities that were remeasured. Our calculation of the transition tax is subject to further refinement as more information is gathered from our foreign subsidiaries, estimates used in the calculation are resolved, and as states provide guidance on how the transition tax may or may not apply in their respective jurisdictions. The reduction of the deferred tax asset related to executive compensation may be changed based upon actual 2018 compensation as compared to our projections of compensation that may be limited. Finally, the Tax Act also imposes a minimum tax on certain foreign subsidiaries deemed to be in excess of a routine return based on tangible asset investment, which is designed to discourage income shifting by subjecting certain foreign intangibles and other income to current U.S. tax. Effective for tax years beginning after 2017, U.S. shareholders of certain foreign corporations are subject to current U.S. tax on their global intangible low-taxes income (GILTI). We have not yet evaluated our potential liability, if any, under the minimum tax for GILTI in 2018 or future years. Accordingly, we have not yet made an accounting policy election either to account for these effects in the future period when the tax arises or to recognize them as part of the deferred taxes. Pursuant to SAB 118, the Company will complete the accounting for the tax effects of all of the provisions of the Tax Act within the required measurement period not to extend beyond one year from the enactment date.

Employee Benefit Plans	12 Months Ended
Employee Benefit Plans	Dec. 31, 2017
Retirement Benefits [Abstract]
Employee Benefit Plans	Employee Benefit Plans The Company provides a 401(k) savings plan for eligible U.S. based employees. Employee contributions are discretionary up to the IRS limits each year and catch up contributions are allowed for employees 50 years of age or older. Under the 401(k) plan, employees become eligible to participate on the first day of the month after three months of continuous service. Under this plan, the Company matches 50% of the employee’s contributions up to 6% of the employee’s annual compensation, as defined by the plan. There is a five-year vesting schedule for the Company match. The Company’s contribution to the plan was $3.7 million, $2.0 million, $3.5 million and $3.0 million for the year ended December 31, 2017, the transition period ended December 31, 2016 and the years ended May 31, 2016 and 2015, respectively. The Company participates with other employers in contributing to the Boilermaker-Blacksmith National Pension Trust (EIN 48-6168020) (“Boilermakers”) and Plumbers and Pipefitters National Pension Fund (EIN 52-6152779) (“Pipefitters”), multi-employer defined benefit pension plans, which covers certain U.S. based union employees. The plans provide multiple plan benefits with corresponding contribution rates that are collectively bargained between participating employers and their affiliated Boilermakers and Pipefitters local unions. Both the Boilermakers and Pipefitters plans are between 65 percent and 80 percent funded as of the latest Form 5500 filed. The Company’s contributions to the Boilermakers and Pipefitters plans, collectively, were $2.4 million, $1.5 million, $2.5 million and $2.5 million for the year ended December 31, 2017, the transition period ended December 31, 2016 and the years ended May 31, 2016 and 2015. These contributions represented less than five percent of total contributions made to the plans. The Company has benefit plans covering certain employees in selected foreign countries. Amounts charged to expense under these plans were not significant in any year.

Related Party Transactions	12 Months Ended
Related Party Transactions	Dec. 31, 2017
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions On August 17, 2016, the Company entered into an agreement with its then Chairman, CEO and Director, Dr. Sotirios Vahaviolos, to purchase up to 1 million of his shares, commencing in October 2016. Refer to Note 20 for further details of the treasury stock repurchases from Dr. Vahaviolos. The Company leases its headquarters under an operating lease from a shareholder and officer of the Company. On August 1, 2014, the Company extended its lease at its headquarters requiring monthly payments through October 2024. Total rent payments made during the year ended December 31, 2017 were approximately $0.9 million. See Note 18 — Commitments and Contingencies for further detail related to operating leases. The Company has a lease for office space located in France, which is partly owned by a shareholder and officer. Total rent payments made during the year ended December 31, 2017 were approximately $0.2 million. The Company has a lease for office space located in Brazil, which is partly owned by a shareholder and officer. Total rent payments made during the year ended December 31, 2017 were approximately $0.1 million. The Company receives benefits consulting services from Capital Management Enterprise (“CME”), which is owned by one of its non-employee directors, Manuel N. Stamatakis. The Company does not pay any fees directly to CME. Any compensation CME receives is from third-party benefit providers.

Obligations under Capital Leases

12 Months Ended

Dec. 31, 2017

Leases [Abstract]

Obligations under Capital Leases

The Company leases certain office space, and service equipment under capital leases, requiring monthly payments ranging from less than $1 thousand to $73 thousand, including effective interest rates that range from approximately 1% to 7% expiring through June 2029. The net book value of assets under capital lease obligations was $19.5 million and $17.6 million at December 31, 2017 and December 31, 2016, respectively.

Scheduled future minimum lease payments subsequent to December 31, 2017 are as follows:



2018	$	5,899
2019	3,788
2020	2,485
2021	1,778
2022	634
Thereafter	760
Total minimum lease payments	15,344
Less: amount representing interest	(731		)
Present value of minimum lease payments	14,613
Less: current portion of obligations under capital leases	(5,875		)
Obligations under capital leases, net of current portion	$	8,738

Commitments and Contingencies

12 Months Ended

Dec. 31, 2017

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

Operating Leases

The Company is party to various non-cancelable operating lease agreements, primarily for its international and domestic office and lab space. Future minimum lease payments under noncancelable operating leases in each of the five years and thereafter subsequent to December 31, 2017 are as follows:



2018	$	11,542
2019	8,888
2020	6,902
2021	4,881
2022	4,304
Thereafter	12,915
Total	$	49,432

Total rent expense was $11.8 million, $6.6 million, $11.2 million and $10.6 million for the year ended December 31, 2017, the transition period ended December 31, 2016 and the years ended May 31, 2016 and 2015, respectively.

Legal Proceedings and Government Investigations

The Company is subject to periodic lawsuits, investigations and claims that arise in the ordinary course of business. The Company cannot predict with certainty the ultimate resolution of lawsuits, investigations and claims asserted against it. Except for the matters described below, the Company does not believe that any currently pending legal proceeding to which the Company is a party will have a material adverse effect on its business, results of operations, cash flows or financial condition. The costs of defense and amounts that may be recovered against the Company may be covered by insurance for certain matters.

Litigation and Commercial Claims

The Company was a defendant in a consolidated class and collective action, Edgar Viceral and David Kruger v Mistras Group, et al, pending in the U.S. District Court for the Northern District of California, originally filed in April 2015. The Company settled the consolidated class and collective action that resulted in the Company recording a pre-tax charge of $6.3 million in the fourth quarter of fiscal 2016, and the Company paid the settlement in the quarter ended March 31, 2017.

The Company was a defendant in the lawsuit AGL Services Company v. Mistras Group, Inc., pending in U.S. District Court for

the Northern District of Georgia, filed November 2016. The case involved radiography work performed by the Company in

2012 on the construction of a pipeline project in the U.S. The owner of the pipeline project claimed damages of approximately $5.8 million. At a trial concluded on October 26, 2017, the jury awarded the plaintiff its damage claim plus interest, which the Company believes is fully covered by insurance.

The Company’s subsidiary in France has been involved in a dispute with a former owner of a business in France purchased by the Company’s French subsidiary. The former owner received a judgment in his favor in the amount of approximately $0.4 million for payment of the contingent consideration portion of the purchase price for the business. The Company recorded a reserve for the full amount of the judgment during the three months ended June 30, 2016. The Company’s subsidiary appealed the judgment and the entire judgment was overturned on appeal, however the full appeals process is not yet completed, and therefore, we have not adjusted the reserve as of December 31, 2017.

The Company was a defendant in a lawsuit, Triumph Aerostructures, LLC d/b/a Triumph Aerostructures-Vought Aircraft Division v. Mistras Group, Inc., pending in Texas State district court, 193rd Judicial District, Dallas County, Texas, filed September 2016. The plaintiff alleged that in 2014 Mistras delivered a defective Ultrasonic inspection system and alleged damages of approximately $2.3 million, the amount it paid for the system. In January 2018, the Company agreed to settle this matter for a payment of $1.6 million and Mistras subsequently obtained ownership of the underlying ultrasonic inspection system. A charge for $1.6 million was recorded in 2017 and payment was made in February 2018.

Government Investigations

In May 2015, the Company received a notice from the U.S. Environmental Protection Agency (“EPA”) that it performed a preliminary assessment at a leased facility the Company operates in Cudahy, California. Based upon the preliminary assessment, the EPA is conducting an investigation of the site, which includes taking groundwater and soil samples. The purpose of the investigation is to determine whether any hazardous materials were released from the facility. The Company has been informed that certain hazardous materials and pollutants have been found in the ground water in the general vicinity of the site and the EPA is attempting to ascertain the origination or source of these materials and pollutants. Given the historic industrial use of the site, the EPA determined that the site of the Cudahy facility should be examined, along with numerous other sites in the vicinity. At this time, the Company is unable to determine whether it has any liability in connection with this matter and if so, the amount or range of any such liability, and accordingly, has not established any reserves for this matter.

Other Potential Contingencies

Some the Company’s workforce is unionized and the terms of employment for these workers are governed by collective bargaining agreements, or CBAs. Under these CBAs, the Company’s subsidiaries are required to contribute to the national pension funds for the unions representing these employees, which are multi-employer pension plans. The Company was notified that a significant project was awarded to another contractor in early 2018, and as a result, the Company and its subsidiaries may experience a significant reduction in the number of its employees covered by CBAs. Under certain circumstances, such a reduction in the number of employees participating in a multi-employer pension plan could result in a complete or partial withdrawal liability to these multi-employer pension plans under ERISA. Presently, the Company is uncertain when or whether its subsidiaries will incur withdrawal liability and, if such liability is incurred, whether it will be material.

Acquisition-related contingencies

The Company is liable for contingent consideration in connection with certain of its acquisitions. As of December 31, 2017, total potential acquisition-related contingent consideration ranged from zero to $8.5 million and would be payable upon the achievement of specific performance metrics by certain of the acquired companies over the next 2.5 years of operations. See Note 7 - Acquisitions to these consolidated financial statements for further information with respect to the Company’s acquisitions completed during the year ended December 31, 2017 and the transition period ended December 31, 2016.

Segment Disclosure

12 Months Ended

Dec. 31, 2017

Segment Reporting [Abstract]

Segment Disclosure

The Company’s three operating segments are:


•	Services. This segment provides asset protection solutions predominantly in North America, with the largest concentration in the United States, followed by Canada, consisting primarily of non-destructive testing, and inspection and engineering services that are used to evaluate the structural integrity and reliability of critical energy, industrial and public infrastructure.


•	International. This segment offers services, products and systems similar to those of the other segments to select markets within Europe, the Middle East, Africa, Asia and South America, but not to customers in China and South Korea, which are served by the Products and Systems segment.


•	Products and Systems. This segment designs, manufactures, sells, installs and services the Company’s asset protection products and systems, including equipment and instrumentation, predominantly in the United States.

Costs incurred for general corporate services, including finance, legal, and certain other costs that are provided to the segments are reported within Corporate and eliminations. Sales to the International segment from the Products and Systems segment and subsequent sales by the International segment of the same items are recorded and reflected in the operating performance of both segments. Additionally, engineering charges and royalty fees charged to the Services and International segments by the Products and Systems segment are reflected in the operating performance of each segment. All such intersegment transactions are eliminated in the Company’s consolidated financial reporting.

The accounting policies of the reportable segments are the same as those described in Note 2 — Summary of Significant Accounting Policies. Segment income from operations is one of the primary performance measures used by the Chief Executive Officer, who is the chief operating decision maker, to assess the performance of each segment and make decisions as to resource allocations. Certain general and administrative costs such as human resources, information technology and training are allocated to the segments. Segment income from operations excludes interest and other financial charges and income taxes. Corporate and other assets are comprised principally of cash, deposits, property, plant and equipment, domestic deferred taxes, deferred charges and other assets. Corporate loss from operations consists of administrative charges related to corporate personnel and other charges that cannot be readily identified for allocation to a particular segment.

Selected financial information by segment for the periods shown was as follows (intercompany transactions are eliminated in Corporate and eliminations):



	For the year ended December 31,			For the Transition Period ended December 31,			For the year ended May 31,
	2017			2016			2016			2015
Revenues
Services	$	543,565		$	293,218		$	553,279		$	540,224
International	144,265			104,013			143,025			146,953
Products and Systems	23,297			14,541			30,293			31,255
Corporate and eliminations	(10,157		)	(7,611		)	(7,416		)	(7,180		)
	$	700,970		$	404,161		$	719,181		$	711,252



	For the year ended December 31,			For the Transition Period ended December 31,		For the year ended May 31,
	2017			2016		2016		2015
Gross profit
Services	$	139,160		$	75,784	$	145,262	$	135,201
International	38,974			34,210		43,613		34,572
Products and Systems	9,798			6,920		14,022		14,314
Corporate and eliminations	(220		)	90		111		646
	$	187,712		$	117,004	$	203,008	$	184,733



	For the year ended December 31,			For the Transition Period ended December 31,			For the year ended May 31,
	2017			2016			2016			2015
Income from operations
Services	$	46,677		$	22,411		$	52,552		$	49,142
International	3,537			10,597			9,293			(575		)
Products and Systems	(16,991		)	(254		)	2,688			2,461
Corporate and eliminations	(29,063		)	(15,221		)	(21,356		)	(20,675		)
	$	4,160		$	17,533		$	43,177		$	30,353



	For the year ended December 31,			For the Transition Period ended December 31,			For the year ended May 31,
	2017			2016			2016			2015
Depreciation and amortization
Services	$	21,649		$	12,765		$	22,725		$	22,268
International	7,768			5,306			7,774			8,451
Products and Systems	2,180			1,372			2,323			2,426
Corporate and eliminations	(214		)	(244		)	(348		)	141
	$	31,383		$	19,199		$	32,474		$	33,286



	December 31,
	2017		2016
Intangible assets, net
Services	$	46,864	$	19,550
International	13,899		14,139
Products and Systems	2,261		5,482
Corporate and eliminations	715		836
	$	63,739	$	40,007



	December 31,
	2017		2016
Total assets
Services	$	377,585	$	291,539
International	150,779		130,427
Products and Systems	12,733		28,964
Corporate and eliminations	13,344		18,497
	$	554,441	$	469,427

Revenue and long-lived assets by geographic area was as follows:



	For the year ended December 31,		For the Transition Period ended December 31,		For the year ended May 31,
	2017		2016		2016		2015
Revenue
United States	$	466,683	$	256,926	$	519,361	$	491,818
Other Americas	86,870		41,777		67,809		68,628
Europe	132,421		91,847		118,566		137,071
Asia-Pacific	14,996		13,611		13,445		13,735
	$	700,970	$	404,161	$	719,181	$	711,252



	December 31,
	2017		2016
Long-lived assets
United States	$	237,616	$	186,960
Other Americas	36,011		29,065
Europe	80,693		67,072
	$	354,320	$	283,097

Repurchase of Common Stock	12 Months Ended
Repurchase of Common Stock	Dec. 31, 2017
Equity [Abstract]
Repurchase of Common Stock	Repurchase of Common Stock On October 7, 2015, the Company's Board of Directors approved a $50 million stock repurchase plan. As part of this plan, on August 17, 2016, the Company entered into an agreement with its Chairman and then CEO, Dr. Sotirios Vahaviolos, to purchase up to 1 million of his shares, commencing in October 2016. Pursuant to the agreement, in general, the Company agreed to purchase from Dr. Vahaviolos up to $2 million of shares each month, at a 2% discount to the average daily price of the Company's common stock for the preceding month. During the transition period ended December 31, 2016, the Company purchased approximately 274,000 shares from Dr. Vahaviolos at an average price of $21.90 per share and an aggregate cost of $6.0 million as well as 146,000 shares in the open market at an average price of $20.48 per share and an aggregate cost of approximately $3.0 million. During the year ended December 31, 2017, the Company purchased approximately 726,000 shares from Dr. Vahaviolos at an average price of $21.93 per share and an aggregate cost of $15.9 million. From the inception of the plan through December 31, 2017, the Company purchased 1,000,000 shares from Dr. Vahaviolos at an average price of $21.92 per share for an aggregate cost of approximately $21.9 million. The Company retired all of its repurchased shares during the fourth quarter of 2017 and they are not included in common stock issued and outstanding as of December 31, 2017. As of December 31, 2017, approximately $25.1 million remained available to repurchase shares under the stock repurchase plan.

Twelve Months Ended December 31, 2016 and Seven Months Ended December 31, 2015 Comparative Data (Unaudited)

12 Months Ended

Dec. 31, 2017

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Twelve Months Ended December 31, 2016 and Seven Months Ended December 31, 2015 Comparative Data (Unaudited)

TWELVE MONTHS ENDED DECEMBER 31, 2016 AND SEVEN MONTHS ENDED DECEMBER 31, 2015 COMPARATIVE DATA (Unaudited)

The condensed consolidated statement of income for the twelve months ended December 31, 2016 and the seven months ended December 31, 2015 is as follows:



	Twelve Months Ended December 31, 2016			Seven Months Ended December 31, 2015
	(unaudited)
Revenues	$	684,762		$	427,913
Cost of revenues	468,929			292,718
Depreciation	21,699			12,005
Gross profit	194,134			123,190
Selling, general and administrative expenses	148,914			81,117
Research and engineering	2,670			1,431
Depreciation and amortization	10,689			6,503
Litigation charges	6,320			—
Acquisition-related benefit, net	(5		)	(959		)
Income from operations	25,546			35,098
Interest expense, net	3,075			3,672
Income before provision for income taxes	22,471			31,426
Provision for income taxes	8,008			11,627
Net income	14,463			19,799
Less: Net income (loss) attributable to non-controlling interests	54			(15		)
Net income available to Mistras Group, Inc. shareholders	$	14,409		$	19,814
Net income per share: Basic	$	0.50		$	0.69
Net income per share: Diluted	$	0.48		$	0.67
Weighted average shares outstanding:
Basic	28,960			28,810
Diluted	30,114			29,676

Selected Quarterly Financial Information (unaudited)

12 Months Ended

Dec. 31, 2017

Quarterly Financial Information Disclosure [Abstract]

Selected Quarterly Financial Information (unaudited)

The following is a summary of the quarterly results of operations for calendar years 2017 and 2016.



Fiscal quarter ended	December 31, 2017		September 30, 2017			June 30, 2017		March 31, 2017
Revenues	$	187,643	$	179,570		$	170,439	$	163,318
Gross Profit	50,319		47,897			46,343		43,153
Income (loss) from operations	6,282		(10,375		)	5,003		3,250
Net income (loss) attributable to Mistras Group, Inc.	$	884	$	(6,968	)	$	2,217	$	1,692
Earnings (loss) per common share:
Basic	$	0.03	$	(0.25	)	$	0.08	$	0.06
Diluted	$	0.03	$	(0.25	)	$	0.07	$	0.06



Fiscal quarter ended	December 31, 2016		September 30, 2016		June 30, 2016		March 31, 2016
Revenues	$	170,156	$	168,811	$	178,340	$	167,455
Gross Profit	47,978		50,651		51,535		43,970
Income from operations	2,944		12,116		4,840		5,646
Net income attributable to Mistras Group, Inc.	$	963	$	7,238	$	2,761	$	3,447
Earnings per common share:
Basic	$	0.03	$	0.25	$	0.10	$	0.12
Diluted	$	0.03	$	0.24	$	0.09	$	0.11

Summary of Significant Accounting Policies (Policies)	12 Months Ended
Summary of Significant Accounting Policies (Policies)	Dec. 31, 2017
Accounting Policies [Abstract]
Principles of Consolidation	Principles of Consolidation The accompanying audited consolidated financial statements include the accounts of Mistras Group, Inc. and its wholly and majority-owned subsidiaries. For subsidiaries in which the Company’s ownership interest is less than 100%, the non-controlling interests are reported in stockholders’ equity in the accompanying consolidated balance sheets. The non-controlling interests in net income, net of tax, is classified separately in the accompanying consolidated statements of income. On January 3, 2017, the Company's Board of Directors approved a change in the Company's fiscal year from May 31 to December 31, effective December 31, 2016. In connection with this change, we previously filed a Transition Report on Form 10-K to report the results of the seven-month transition period from June 1, 2016 to December 31, 2016. In this Annual Report, the periods presented are the year ended December 31, 2017, the seven-month transition period from June 1, 2016 to December 31, 2016 and the years ended May 31, 2016 and 2015. The Company has also included unaudited data for the year ended December 31, 2016 and for the seven months ended December 31, 2015 (See Note 21). All significant intercompany accounts and transactions have been eliminated in consolidation. For fiscal 2016 and 2015, Mistras Group, Inc.’s and its subsidiaries’ fiscal years ended on May 31 except for the subsidiaries in the International segment, which ended on April 30. Accordingly, the Company’s International segment subsidiaries were consolidated on a one-month lag. Therefore, in the quarter and year of acquisition, results of acquired subsidiaries in the International segment were generally included in consolidated results for one less month than the actual number of months from the acquisition date to the end of the reporting period. As discussed in Note 7 - Acquisitions and Dispositions, during the lag period in fiscal 2015, the Company sold an international subsidiary, and decided to sell two additional international subsidiaries. Effective December 31, 2016, the Company's International segment is no longer consolidated on a one month lag, and such change for the seven month transition period ended December 31, 2016 was not material.
Reclassifications	Reclassifications Certain amounts in prior periods have been reclassified to conform to the current year presentation. Such reclassifications did not have a material effect on the Company's financial condition or results of operations as previously reported.
Revenue Recognition	Revenue Recognition Revenue is generally recognized when persuasive evidence of an arrangement exists, services have been rendered or products have been delivered, the fee is fixed or determinable, and collectability is reasonably assured. Shipping and handling costs are included in cost of revenues. Taxes collected from customers and remitted to governmental authorities are presented in the consolidated statements of income on a net basis. One customer accounted for 11% and 12% of our revenues for the year ended December 31, 2017 and the transition period ended December 31, 2016, which primarily were generated from the Services segment. One customer accounted for 10% of our revenues in fiscal 2016, which primarily were generated from the Services segment. No customer accounted for 10% or more of our revenues in fiscal 2015. The following revenue recognition policies define the manner in which we account for specific transaction types: Services Most of our projects are short-term in nature and revenue is primarily derived from providing services on a time and material basis. Service arrangements generally consist of inspection professionals working under contract for a fixed period of time or on a specific customer project. Revenue is generally recognized when the service is performed in accordance with terms of each customer arrangement, upon completion of the earnings process and when collection is reasonably assured. At the end of any reporting period, earned revenue is accrued for services that have been provided which have not yet been billed. Reimbursable costs, including those related to travel and out-of-pocket expenses, are included in revenue, and equivalent amounts of reimbursable costs are included in cost of services. Products and Systems Sales of products and systems are recorded when the sales price is fixed and determinable and the risks and rewards of ownership are transferred (generally upon shipment) and when collectability is reasonably assured. These arrangements occasionally contain multiple elements or deliverables, such as hardware, software (that is essential to the functionality of the hardware) and related services. The Company recognizes revenue for delivered elements as separate units of accounting, when the delivered elements have standalone value, uncertainties regarding customer acceptance are resolved and there are no refund or return rights for the delivered elements. The Company establishes the selling prices for each deliverable based on vendor-specific objective evidence (“VSOE”), if available, third-party evidence, if VSOE is not available, or estimated selling price (“ESP”) if neither VSOE nor third-party evidence is available. The Company establishes VSOE of selling price using the price charged for a deliverable when sold separately and, in rare instances, using the price established by management having the relevant authority. Third-party evidence of selling price is established by evaluating largely similar and interchangeable competitor products or services in standalone sales to similarly situated customers. The Company determines ESP, by considering internal factors such as margin objectives, pricing practices and controls, customer segment pricing strategies and the product life cycle. Consideration is also given to market conditions such as competitor pricing strategies and industry technology life cycles. When determining ESP, the Company applies management judgment to establish margin objectives and pricing strategies and to evaluate market conditions and product life cycles. Changes in the aforementioned factors may result in a different allocation of revenue to the deliverables in multiple element arrangements and therefore may change the pattern and timing of revenue recognition for these elements, but will not change the total revenue recognized for the arrangement. A portion of the Company’s revenue is generated from engineering and manufacturing of custom products under long-term contracts that may last from several months to several years, depending on the contract. Revenues from long-term contracts are recognized on the percentage-of-completion method of accounting. Under the percentage-of-completion method of accounting revenues are recognized as work is performed. The percentage of completion at any point in time is generally based on total costs or total labor dollars incurred to date in relation to the total estimated costs or total labor dollars estimated at completion. The percentage of completion is then applied to the total contract revenue to determine the amount of revenue to be recognized in the period. Application of the percentage-of-completion method of accounting requires the use of estimates of costs to be incurred for the performance of the contract. Contract costs include all direct materials, direct labor costs and those indirect costs related to contract performance, such as indirect labor, supplies, tools, repairs, and all costs associated with operation of equipment. The cost estimation process is based upon the professional knowledge and experience of our engineers, project managers and financial professionals. Factors that are considered in estimating the work to be completed include the availability and productivity of labor, the nature and complexity of the work to be performed, the effect of change orders, the availability of materials, the effect of any delays in our project performance and the recoverability of any claims. Whenever revisions of estimated contract costs and contract values indicate that the contract costs will exceed estimated revenues, thus creating a loss, a provision for the total estimated loss is recorded in that period.
Use of Estimates	Use of Estimates The preparation of financial statements in accordance with generally accepted accounting principles requires that the Company make estimates and assumptions that affect the reported amounts of assets, liabilities, revenue and expenses and disclosure of contingent assets and liabilities at the date of financial statements. The Company bases its estimates and assumptions on historical experience, known or expected trends and various other assumptions that it believes to be reasonable. As future events and their effects cannot be determined with precision, actual results could differ significantly from these estimates, which may cause the Company’s future results to be significantly affected.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly liquid investments purchased with an original maturity of three months or less to be cash equivalents.
Accounts Receivable	Accounts Receivable Accounts receivable are stated net of an allowance for doubtful accounts and sales allowances. Outstanding accounts receivable balances are reviewed periodically, and allowances are provided at such time that management believes it is probable that such balances will not be collected within a reasonable period of time. The Company extends credit to its customers based upon credit evaluations in the normal course of business, primarily with 30-day terms. Bad debts are provided for based on historical experience and management’s evaluation of outstanding accounts receivable. Accounts are written off when they are deemed uncollectible.
Inventories	Inventories Inventories are stated at the lower of cost, as determined by using the first-in, first-out method, or market. Work in process and finished goods inventory include material, direct labor, variable costs and overhead.
Purchased and Internal-Use Software	Purchased and Internal-Use Software The Company capitalizes certain costs that are incurred to purchase or to create and implement internal-use software, which includes software coding, installation and testing. Capitalized costs are amortized on a straight-line basis over three years, the estimated useful life of the software.
Property, Plant and Equipment	Property, Plant and Equipment Property, plant and equipment are recorded at cost. Depreciation of property, plant and equipment is computed utilizing the straight-line method over the estimated useful lives of the assets. Amortization of leasehold improvements is computed utilizing the straight-line method over the shorter of the remaining lease term or estimated useful life. Repairs and maintenance costs are expensed as incurred.
Goodwill	Goodwill Goodwill represents the excess purchase price of acquired businesses over the fair values attributed to underlying net tangible assets and identifiable intangible assets. We test goodwill for impairment at a “reporting unit” level (which for the Company is represented by (i) our Services segment, (ii) our Products and Systems segment, and (iii) the European component and (iv) Brazilian component of our International segment). Our annual impairment test is conducted on the first day of our fourth quarter. In connection with the change in our fiscal year to December 31, our annual test date is October 1. For the transition period ended December 31, 2016, a December 1 date was used and historically, prior to the fiscal year end change, the Company tested for impairment annually as of March 1. Goodwill is also tested for impairment whenever an event occurs or circumstances change that would more likely than not reduce the fair value of a reporting unit below its carrying amount. During the third quarter of 2017, there was a triggering event in the Products and Systems segment that resulted in a $13.2 million goodwill impairment charge. See Note 8 for further details. If the fair value of a reporting unit is less than its carrying value, this is an indicator that the goodwill assigned to that reporting unit may be impaired. As a result of the Company adopting ASU 2017-04, impairment will be recorded in the amount that fair value is less than carrying value, as the ASU eliminated step two of goodwill impairment process. The Company considers the income and market approaches to estimating the fair value of our reporting units, which requires significant judgment in evaluation of economic and industry trends, estimated future cash flows, discount rates and other factors.
Impairment of Long-lived Assets	Impairment of Long-lived Assets The Company reviews the recoverability of its long-lived assets (or asset groups) on a periodic basis in order to identify indicators of a possible impairment. The assessment for potential impairment is based primarily on the Company’s ability to recover the carrying value of its long-lived assets from expected future undiscounted cash flows. If the total expected future undiscounted cash flows are less than the carrying amount of the assets, a loss is recognized for the difference between fair value (computed based upon the expected future discounted cash flows) and the carrying value of the assets.
Research and Engineering	Research and Engineering Research and product development costs are expensed as incurred.
Advertising, Promotions and Marketing	Advertising, Promotions and Marketing The costs for advertising, promotion and marketing programs are expensed as incurred and are included in selling, general and administrative expenses.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The carrying amounts of cash and cash equivalents, accounts receivable, accounts payable and other financial current assets and liabilities approximate fair value based on the short-term nature of the items. The carrying value of long-term debt approximates fair value due to the variable-rate structure of the debt. The fair value of the Company’s notes payable and capital lease obligations approximate their carrying amounts as those obligations bear interest at rates which management believes would currently be available to the Company for similar obligations.
Foreign Currency Translation	Foreign Currency Translation The financial position and results of operations of the Company’s foreign subsidiaries are measured using their functional currencies, which are their local currencies. Assets and liabilities of foreign subsidiaries are translated into the U.S. Dollar at the exchange rates in effect at the balance sheet date. Income and expenses are translated at the average exchange rate during the period. Translation gains and losses are reported as a component of other comprehensive (loss) income for the period and included in accumulated other comprehensive (loss) income within stockholders’ equity.
Concentrations of Credit Risk	Concentrations of Credit Risk Financial instruments that potentially subject the Company to concentrations of credit risk consist principally of cash and cash equivalents and accounts receivable. At times, cash deposits may exceed the limits insured by the Federal Deposit Insurance Corporation. The Company believes it is not exposed to any significant credit risk or risk of nonperformance of financial institutions.
Self-Insurance	Self-Insurance The Company is self-insured for certain losses relating to workers’ compensation and health benefits claims. The Company maintains third-party excess insurance coverage for all workers' compensation and health benefit claims in excess of approximately $0.3 million per occurence to reduce its exposure from such claims. Self-insured losses are accrued when it is probable that an uninsured claim has been incurred but not reported and the amount of the loss can be reasonably estimated at the balance sheet date.
Share-based Compensation	Share-based Compensation The value of services received from employees and directors in exchange for an award of an equity instrument is measured based on the grant-date fair value of the award. Such value is recognized as a non-cash expense on a straight-line basis over the period the individual provides services, which is typically the vesting period of the award with the exception of awards with graded vesting that contain an internal performance measure where each tranche is recognized on a straight-line basis over its vesting period subject to the probability of meeting the performance requirements and adjusted for the number of shares expected to be earned. As share-based compensation expense is based on awards ultimately expected to vest, the amount of expense has been reduced for estimated forfeitures. The cost of these awards is recorded in selling, general and administrative expense in the Company’s consolidated statements of income.
Income Taxes	Income Taxes Income taxes are accounted for under the asset and liability method. Deferred income tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases and tax credit carry-forwards. Deferred income tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred income tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date. A valuation allowance is provided if it is more likely than not that some or all of a deferred income tax asset will not be realized. Financial accounting standards prescribe a minimum recognition threshold a tax position is required to meet before being recognized in the financial statements. These standards also provide guidance on de-recognition, measurement, and classification of amounts relating to uncertain tax positions, accounting for and disclosure of interest and penalties, accounting in interim periods and disclosures required. Interest and penalties related to unrecognized tax positions are recognized as incurred within “provision for income taxes” in the consolidated statements of income.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In August 2015, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") 2015-14, Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date, which defers the effective date of ASU 2014-09 for all entities by one year. This update is effective for public business entities for annual reporting periods beginning after December 15, 2017, including interim periods within those reporting periods. Earlier application is permitted only as of annual reporting periods beginning after December 15, 2016, including interim reporting periods within that reporting period. ASU 2014-09 will become effective for the Company beginning 2018. The ASU permits two methods of adoption: retrospectively to each prior reporting period presented (full retrospective method), or retrospectively with the cumulative effect of initially applying the guidance recognized at the date of initial application (the cumulative catch-up transition method). The ASU also requires expanded disclosures relating to the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. Additionally, qualitative and quantitative disclosures are required about customer contracts, significant judgments and changes in judgments, and assets recognized from the costs to obtain or fulfill a contract. The Company adopted ASU 2014-09 along with the related additional ASU’s on Topic 606 on January 1, 2018, utilizing the cumulative catch-up method. The result of adoption is immaterial to the Company's consolidated financial statements, largely because most of our projects are short-term in nature and billed on a time and material basis. The Company utilizes a practical expedient that provides for revenue to be recognize in an amount that corresponds directly with the value to the customer of the entity’s performance completed to date. The Company will make the additional required disclosures under Topic 606, starting with the Company's condensed consolidated financial statements in the first quarter of 2018. In November 2015, the FASB issued ASU No. 2015-17, Income Taxes (Topic 740): Balance Sheet Classification of Deferred Taxes. This amendment will simplify the presentation of deferred tax assets and liabilities on the balance sheet and require all deferred tax assets and liabilities to be treated as non-current. ASU 2015-17 is effective for fiscal years, and interim periods within those fiscal years beginning after December 15, 2016, with early adoption permitted. The Company adopted this guidance prospectively beginning in the first quarter of 2017, which did not have a material impact on the consolidated financial statements and related disclosures. In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842). This amendment supersedes previous accounting guidance (Topic 840) and requires all leases, with the exception of leases with a term of 12 months or less, to be recorded on the balance sheet as lease assets and lease liabilities. ASU 2016-02 is effective for fiscal years, and interim periods within those fiscal years beginning after December 15, 2018, with early adoption permitted. The standard requires lessees and lessors to recognize and measure leases at the beginning of the earliest period presented using a modified retrospective approach. The Company is evaluating the effect that ASU 2016-02 will have on its consolidated financial statements and related disclosures. In March 2016, the FASB issued ASU No. 2016-09, Stock Compensation (Topic 718). This amendment simplifies certain aspects of accounting for share-based payment transactions, which include accounting for income taxes and the related impact on the statement of cash flows, an option to account for forfeitures when they occur in addition to the existing guidance to estimate the forfeitures of awards, classification of awards as either equity or liabilities and classification on the statement of cash flows for employee taxes paid to tax authorities on shares withheld for vesting. ASU 2016-09 is effective for fiscal years, and interim periods within those fiscal years beginning after December 15, 2016, with early adoption permitted. The Company adopted this guidance prospectively beginning in the first quarter of 2017, and accordingly, is recording excess tax benefits and tax deficiencies as a component of income tax expense. In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (Topic 230). This amendment will provide guidance on the presentation and classification of specific cash flow items to improve consistency within the statement of cash flows. ASU 2016-15 is effective for fiscal years, and interim periods within those fiscal years beginning after December 15, 2017, with early adoption permitted. The Company does not expect that ASU 2016-15 will have a material impact on its consolidated financial statements and related disclosures. In November 2016, the FASB issued ASU No. 2016-18, Statement of Cash Flows (Topic 230). This amendment will clarify the presentation of restricted cash on the statement of cash flows. Amounts generally described as restricted cash and restricted cash equivalents should be included with cash and cash equivalents when reconciling the beginning and ending cash balances on the statement of cash flows. ASU 2016-18 is effective for fiscal years, and interim periods within those fiscal years beginning after December 15, 2017, with early adoption permitted. The Company does not expect that ASU 2016-18 will have a material impact on its consolidated financial statements and related disclosures. In January 2017, the FASB issued ASU No. 2017-04, Intangibles-Goodwill and Other (Topic 350). This amendment eliminates Step Two of the goodwill impairment test. Under the amendments in this update, entities should perform the annual goodwill impairment test by comparing the carrying value of its reporting units to their fair value. An entity should record an impairment charge for the amount by which the carrying amount exceeds the reporting unit’s fair value. Tax deductibility of goodwill should be considered in evaluating any reporting unit's impairment loss to be taken. ASU 2017-04 is effective for fiscal years beginning after December 15, 2019, with early adoption permitted. The Company early adopted ASU 2017-04 in the third quarter of 2017 for its consolidated financial statements and related disclosures. See Notes 8 and 9 for information on the impairment of assets in the Products and Systems reporting unit during the three months ended September 30, 2017. In May 2017, the FASB issued ASU 2017-09, Compensation-Stock Compensation (Topic 718) Scope of Modification Accounting. This amendment provides guidance concerning which changes to the terms or conditions of a share-based payment require an entity to apply modification accounting. Certain changes to stock awards, notably administrative changes, do not require modification accounting. There are three specific criteria that need to be met in order to prove that modification accounting is not required. ASU 2017-09 is effective for fiscal years, and interim period within those fiscal years, beginning after December 15, 2017, with early adoption permitted. The Company does not expect that ASU 2017-09 will have a material impact on its consolidated financial statements and related disclosures. In December 2017, the SEC staff issued Staff Accounting Bulletin No. 118 (“SAB 118”), which provides guidance on accounting for the tax effects of the Tax Cuts and Jobs Act (the "Tax Act"). SAB 118 provides a measurement period that should not extend beyond one year from the Tax Act enactment date for companies to complete the accounting under ASC 740. In accordance with SAB 118, a company must reflect the income tax effects of those aspects of the Act for which the accounting under ASC 740 is complete. To the extent that a company’s accounting for certain income tax effects of the Tax Act is incomplete but it is able to determine a reasonable estimate, it must record a provisional estimate in the financial statements. If a company cannot determine a provisional estimate to be included in the financial statements, it should continue to apply ASC 740 on the basis of the provisions of the tax laws that were in effect immediately before the enactment of the Tax Act. The Company considers the accounting for the Tax Act to be provisional as of December 31, 2017. The Company will complete the accounting for the tax effects of all of the provisions of the Tax Act within the required measurement period not to extend beyond one year from the enactment date.
Fair Value Measurement	Fair Value Measurements The Company performs fair value measurements in accordance with the guidance provided by ASC 820, Fair Value Measurements and Disclosures. ASC 820 defines fair value as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. It also establishes a three level hierarchy that prioritizes the inputs used to measure fair value. The three levels of the hierarchy are defined as follows: Level 1 — Inputs are unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date. Level 2 — Observable inputs other than quoted prices included in Level 1, including quoted prices for similar assets or liabilities in active markets, quoted prices for identical assets or liabilities in inactive markets, inputs other than quoted prices that are observable for the asset or liability and inputs derived principally from or corroborated by observable market data. Level 3 — Unobservable inputs reflecting the Company’s own assumptions about inputs that market participants would use in pricing the asset or liability based on the best information available.

Earnings per Share (Tables)

12 Months Ended

Dec. 31, 2017

Earnings Per Share [Abstract]

Schedule of computations of basic and diluted earnings per share

The following table sets forth the computations of basic and diluted earnings per share:



	For the year ended December 31,			For the transition period ended December 31,		For the year ended May 31,
	2017			2016		2016		2015
Basic (loss) earnings per share
Numerator:
Net (loss) income attributable to Mistras Group, Inc.	$	(2,175	)	$	9,568	$	24,654	$	16,081
Denominator
Weighted average common shares outstanding	28,422			28,989		28,856		28,613
Basic (loss) earnings per share	$	(0.08	)	$	0.33	$	0.85	$	0.56

Diluted earnings per share:
Numerator:
Net income attributable to Mistras Group, Inc.	$	(2,175	)	$	9,568	$	24,654	$	16,081
Denominator
Weighted average common shares outstanding	28,422			28,989		28,856		28,613
Dilutive effect of stock options outstanding	—			791		712		719
Dilutive effect of restricted stock units outstanding	—			345		323		258
	28,422			30,125		29,891		29,590
Diluted (loss) earnings per share	$	(0.08	)	$	0.32	$	0.82	$	0.54

Schedule of potential common shares that were excluded from the computation of diluted earnings per share

The following potential common shares were excluded from the computation of diluted earnings per share, as the effect would have been anti-dilutive:



	For the year ended December 31,			For the transition period ended December 31,	For the year ended May 31,
	2017			2016	2016	2015
Potential common stock attributable to stock options outstanding	810	₍₁	₎	—	5	6
Potential common stock attributable to restricted stock units (RSUs) and performance stock units (PSUs) outstanding	353	₍₂	₎	2	24	1
Total	1,163			2	29	7

(1) - 805 shares related to stock options were excluded from the calculation of diluted EPS due to the net loss for the period.

(2) - 351 shares related to RSUs and PSUs were excluded from the calculation of diluted EPS due to the net loss for the period.

Inventories (Tables)

12 Months Ended

Dec. 31, 2017

Inventory Disclosure [Abstract]

Schedule of inventories

Inventories consist of the following:



	December 31,		December 31,
	2017		2016
Raw materials	$	5,105	$	5,054
Work in progress	1,192		1,246
Finished goods	2,746		2,335
Services-related consumable supplies	1,460		1,382
Inventory	$	10,503	$	10,017

Property, Plant and Equipment, net (Tables)

12 Months Ended

Dec. 31, 2017

Property, Plant and Equipment [Abstract]

Schedule of property, plant and equipment

Property, plant and equipment consist of the following:



		December 31,			December 31,
	Useful Life	2017			2016
	(Years)
Land		$	2,414		$	1,714
Building and improvements	30-40	24,003			19,261
Office furniture and equipment	5-8	14,230			9,069
Machinery and equipment	5-7	191,721			169,928
		232,368			199,972
Accumulated depreciation and amortization		(145,225		)	(126,823		)
Property, plant and equipment, net		$	87,143		$	73,149

Acquisitions and Dispositions (Tables)

12 Months Ended

Dec. 31, 2017

Business Combinations [Abstract]

Summary of estimated fair value of assets acquired and liabilities assumed at the date of acquisition

The following table summarizes the estimated fair value of the assets acquired and liabilities assumed, the Company's allocation of purchase price and any subsequent adjustments made during the year ended December 31, 2017 and the transition period ended December 31, 2016:



	Year ended December 31, 2017			Transition Period
Number of entities	3			3

Cash paid	$	83,963		$	8,295
Working capital adjustments	150			—
Notes payable	—			325
Contingent consideration	3,407			1,630
Consideration paid	$	87,520		$	10,250

Current net assets	$	7,165		$	1,632
Debt and other long-term liabilities	(2,848		)	(214		)
Property, plant and equipment	11,115			953
Deferred tax asset (liability)	(1,278		)	392
Intangibles	31,671			3,367
Goodwill	41,695			4,120
Net assets acquired	$	87,520		$	10,250

Schedule of acquisition-related expense, net



	For the year ended December 31,			For the Transition Period ended December 31,		For the year ended May 31,
	2017			2016		2016			2015
Due diligence, professional fees and other transaction costs	$	945		$	231	$	629		$	215
Adjustments to fair value of contingent consideration liabilities	$	(463	)	$	265	$	(2,082	)	$	(5,382	)
Acquisition-related (benefit) expense, net	$	482		$	496	$	(1,453	)	$	(5,167	)

Goodwill (Tables)

12 Months Ended

Dec. 31, 2017

Goodwill and Intangible Assets Disclosure [Abstract]

Schedule of changes in carrying amount of goodwill by segment

The changes in the carrying amount of goodwill by segment is shown below:



	Services			International			Products and Systems			Total
Balance at May 31, 2016	$	119,683		$	36,340		$	13,197		$	169,220
Goodwill acquired during the year	4,120			—			—			4,120
Adjustments to preliminary purchase price allocations	(19		)	—			—			(19		)
Foreign currency translation	(392		)	(2,989		)	—			(3,381		)
Balance at December 31, 2016	$	123,392		$	33,351		$	13,197		$	169,940
Goodwill acquired during the year	41,695			—			—			41,695
Impairment charge	—			—			(13,197		)	(13,197		)
Adjustments to preliminary purchase price allocations	(211		)	—			—			(211		)
Foreign currency translation	925			4,286			—			5,211
Balance at December 31, 2017	$	165,801		$	37,637		$	—		$	203,438

Intangible Assets (Tables)

12 Months Ended

Dec. 31, 2017

Goodwill and Intangible Assets Disclosure [Abstract]

Schedule of gross amount and accumulated amortization of intangible assets

The gross carrying amount and accumulated amortization of intangible assets were as follows:



		December 31,										December 31,
		2017										2016
	Useful Life (Years)	Gross Amount		Accumulated Amortization			Impairment			Net Carrying Amount		Gross Amount		Accumulated Amortization			Net Carrying Amount
Customer relationships	5-14	$	113,299	$	(58,107	)	$	(170	)	$	55,022	$	81,559	$	(50,417	)	$	31,142
Software/Technology	3-15	19,523		(14,133		)	(2,411		)	2,979		18,128		(12,577		)	5,551
Covenants not to compete	2-5	12,510		(10,438		)	—			2,072		11,143		(9,647		)	1,496
Other	2-5	10,109		(6,411		)	(32		)	3,666		7,266		(5,448		)	1,818
Total		$	155,441	$	(89,089	)	$	(2,613	)	$	63,739	$	118,096	$	(78,089	)	$	40,007

Schedule of expected amortization expense of intangible assets

Amortization expense in each of the five years and thereafter subsequent to December 31, 2017 related to the Company’s intangible assets is expected to be as follows:



	Expected Amortization Expense

2018	$	10,117
2019	8,952
2020	7,483
2021	6,411
2022	6,076
Thereafter	24,700
Total	$	63,739

Long-Term Debt (Tables)

12 Months Ended

Dec. 31, 2017

Debt Disclosure [Abstract]

Schedule of long-term debt

Long-term debt consists of the following:



	December 31,
	2017			2016
Senior credit facility	$	156,948		$	82,776
Notes payable	228			320
Other	9,702			4,200
Total debt	166,878			87,296
Less: Current portion	(2,358		)	(1,379		)
Long-term debt, net of current portion	$	164,520		$	85,917

Schedule of principal payments due under all borrowing agreements

Scheduled principal payments due under all borrowing agreements in each of the five years and thereafter subsequent to December 31, 2017 are as follows:



2018	$	2,358
2019	1,664
2020	1,243
2021	892
2022	157,728
Thereafter	2,993
Total	$	166,878

- Definition

Tabular disclosure of long-debt instruments or arrangements, including identification, terms, features, collateral requirements and other information necessary to a fair presentation. These are debt arrangements that originally required repayment more than twelve months after issuance or greater than the normal operating cycle of the entity, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21475-112644

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=75038535&loc=d3e64711-112823

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(e),(f))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21538-112644

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21506-112644

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28541-108399

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21521-112644

+ Details

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

Schedule of Changes in Fair Value, Level 3 Contingent Consideration

The following table represents the changes in the fair value of Level 3 contingent consideration:



Balance at May 31, 2016	$	2,075
Acquisitions	1,630
Payments	(795		)
Accretion of liability	136
Revaluation	126
Foreign currency translation	(78		)
Balance at December 31, 2016	$	3,094
Acquisitions	3,407
Payments	(560		)
Accretion of liability	272
Revaluation	(735		)
Foreign currency translation	30
Balance at December 31, 2017	$	5,508

Share-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2017

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Schedule of cash proceeds from, and the intrinsic value of, stock options exercised

Cash proceeds from, and the intrinsic value of stock options exercised during the year ended December 31, 2017, the transition period ended December 31, 2016 and the years ended May 31, 2016 and 2015 were as follows:



	For the year ended December 31,		For the Transition Period ended December 31,		For the year ended May 31,
	2017		2016		2016		2015
Cash proceeds from options exercised	$	275	$	604	$	543	$	750
Aggregate intrinsic value of options exercised	580		993		658		563

Summary of stock option activity, weighted average exercise prices, options outstanding and exercisable



	For the year ended December 31,				For the Transition Period ended December 31,				For the year ended May 31,
	2017				2016				2016				2015
	Common Stock Options		Weighted Average Exercise Price		Common Stock Options		Weighted Average Exercise Price		Common Stock Options		Weighted Average Exercise Price		Common Stock Options		Weighted Average Exercise Price
Outstanding at beginning of year:	2,167		$	13.33	2,232		$	13.21	2,287		$	13.13	2,352		$	13.09
Granted	—		$	—	—		$	—	—		$	—	—		$	—
Exercised	(37	)	$	7.39	(65	)	$	9.27	(55	)	$	9.87	(65	)	$	11.54
Expired or forfeited	—		$	—	—		$	—	—		$	—	—		$	—
Outstanding at end of year:	2,130		$	13.43	2,167		$	13.33	2,232		$	13.21	2,287		$	13.13

Schedule of information concerning outstanding and exercisable options



			For the year ended December 31, 2017
			Options Outstanding			Options Exercisable
Range of Exercise Prices	Total Options Outstanding		Weighted Average Remaining Life (Years)	Weighted Average Exercise Price		Number Exercisable		Weighted Average Exercise Price
$10.00-$11.54	35		1.1	$	10.54	35		$	10.54
$13.46-$22.35	2,095		1.7	$	13.48	2,095		$	13.48
	2,130					2,130

Aggregate Intrinsic Value	$	21,374				$	21,374

Summary of restricted stock activity



	For the year ended December 31,				For the transition period ended December 31,				For the year ended May 31,
	2017				2016				2016				2015
	Units		Weighted Average Grant-Date Fair Value		Units		Weighted Average Grant-Date Fair Value		Units		Weighted Average Grant-Date Fair Value		Units		Weighted Average Grant-Date Fair Value
Outstanding at beginning of period:	569		$	20.81	575		$	18.85	564		$	20.47	628		$	19.37
Granted	183		$	21.26	219		$	24.48	264		$	16.73	192		$	21.87
Released	(185	)	$	20.49	(207	)	$	19.40	(223	)	$	20.40	(232	)	$	18.17
Forfeited	(35	)	$	21.45	(18	)	$	19.55	(30	)	$	19.26	(24	)	$	20.57
Outstanding at end of period:	532		$	21.05	569		$	20.81	575		$	18.85	564		$	20.47

Summary of performance restricted stock units activity

A summary of the Company's Performance Restricted Stock Unit activity is presented below:



	For the year ended December 31, 2017				For the Transition Period ended December 31, 2016
	Units		Weighted Average Grant-Date Fair Value		Units		Weighted Average Grant-Date Fair Value
Outstanding at beginning of period:	290		$	16.01	328		$	17.02
Granted	128		$	20.42	105		$	24.90
Performance condition adjustments, net	(68	)	$	20.55	(54	)	$	24.49
Released	(72	)	$	15.82	(89	)	$	24.50
Forfeited	—		$	—	—		$	—
Outstanding at end of period:	278		$	17.00	290		$	16.01

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Schedule of income before provision for income taxes

Income before provision for income taxes is as follows:



	For the year ended December 31,			For the Transition Period ended December 31,		For the year ended May 31,
	2017			2016		2016		2015
(Loss) income before provision for income taxes from:
U.S. operations	$	(7,303	)	$	5,116	$	27,772	$	26,893
Foreign operations	7,077			10,365		10,643		(1,162		)
(Loss) Earnings before income taxes	$	(226	)	$	15,481	$	38,415	$	25,731

Schedule of provision for income taxes

The provision for income taxes consists of the following:



	For the year ended December 31,			For the Transition Period ended December 31,			For the year ended May 31,
	2017			2016			2016			2015
Current
Federal	$	3,558		$	1,990		$	9,156		$	8,489
States and local	39			483			1,537			1,177
Foreign	3,131			3,569			3,672			1,493
Reserve for uncertain tax positions	71			(39		)	(529		)	(48		)
Total current	6,799			6,003			13,836			11,111
Deferred
Federal	(3,857		)	6			82			(145		)
States and local	(810		)	(28		)	(51		)	(126		)
Foreign	(437		)	(514		)	(557		)	(2,416		)
Total deferred	(5,104		)	(536		)	(526		)	(2,687		)
Net change in valuation allowance	247			403			455			1,316
Net deferred	(4,857		)	(133		)	(71		)	(1,371		)
Provision for income taxes	$	1,942		$	5,870		$	13,765		$	9,740

Schedule of provision for income taxes computed by applying the statutory federal tax rate

The provision for income taxes differs from the amount computed by applying the statutory federal tax rate to income tax as follows:



	For the year ended December 31,					For the Transition period ended December 31,
	2017					2016
Federal tax at statutory rate	$	(79	)	35.0	%	$	5,418		35.0	%
State taxes, net of federal benefit	(502		)	221.6	%	296			1.9	%
Foreign tax	217			(95.8	)%	(573		)	(3.7	)%
Contingent consideration	(63		)	27.7	%	(4		)	—	%
Permanent differences	377			(166.4	)%	373			2.4	%
Transition tax, net of foreign tax credits	3,942			(1,741.4	)%	—			—	%
Federal tax rate change due to the Tax Act	(1,956		)	864.0	%	—			—	%
Other	(241		)	106.5	%	(43		)	(0.3	)%
Change in valuation allowance	247			(109.1	)%	403			2.6	%
Total provision for income taxes	$	1,942		(857.9	)%	$	5,870		37.9	%



	For the year ended May 31,
	2016					2015
Federal tax at statutory rate	$	13,445		35.0	%	$	9,006		35.0	%
State taxes, net of federal benefit	966			2.5	%	683			2.7	%
Foreign tax	(610		)	(1.6	)%	(517		)	(2.0	)%
Contingent consideration	(425		)	(1.1	)%	(914		)	(3.6	)%
Permanent differences	245			0.6	%	196			0.8	%
Other	(311		)	(0.8	)%	(30		)	(0.1	)%
Change in valuation allowance	455			1.2	%	1,316			5.1	%
Total provision for income taxes	$	13,765		35.8	%	$	9,740		37.9	%

Schedule of deferred income tax assets and liabilities

Deferred income tax attributes resulting from differences between financial accounting amounts and income tax basis of assets and liabilities are as follows:



	December 31,
	2017			2016
Deferred income tax assets
Allowance for doubtful accounts	$	838		$	969
Inventory	265			236
Intangible assets	2,255			2,529
Accrued expenses	2,560			5,157
Net operating loss carryforward	3,729			4,094
Capital lease obligations	1,004			1,140
Capital losses	463			719
Foreign tax credit carryover	618			—
Deferred share-based compensation	4,080			5,802
Other	484			285
Deferred income tax assets	16,296			20,931
Valuation allowance	(4,044		)	(3,896		)
Net deferred income tax assets	12,252			17,035
Deferred income tax liabilities
Property and equipment	(6,893		)	(8,655		)
Goodwill	(6,578		)	(13,586		)
Intangible assets	(5,972		)	(5,051		)
Other	(6		)	(11		)
Deferred income tax liabilities	(19,449		)	(27,303		)
Net deferred income taxes	$	(7,197	)	$	(10,268	)

Summary of changes in Company's gross unrecognized tax benefits, excluding interest and penalties

The following table summarizes the changes in the Company’s gross unrecognized tax benefits, excluding interest and penalties:



	For the year ended December 31,			For the Transition Period ended December 31,
	2017			2016
Balance at beginning of period	$	267		$	303
Additions for tax positions related to the current fiscal period	11			8
Additions for tax positions related to prior years	188			—
Decreases for tax positions related to prior years	—			(11		)
Impact of foreign exchange fluctuation	10			—
Settlements	(198		)	—
Reductions related to the expiration of statutes of limitations	(122		)	(33		)
Balance at end of period	$	156		$	267

Obligations under Capital Leases (Tables)

12 Months Ended

Dec. 31, 2017

Leases [Abstract]

Scheduled future minimum lease payments

Scheduled future minimum lease payments subsequent to December 31, 2017 are as follows:



2018	$	5,899
2019	3,788
2020	2,485
2021	1,778
2022	634
Thereafter	760
Total minimum lease payments	15,344
Less: amount representing interest	(731		)
Present value of minimum lease payments	14,613
Less: current portion of obligations under capital leases	(5,875		)
Obligations under capital leases, net of current portion	$	8,738

Segment Disclosure (Tables)

12 Months Ended

Dec. 31, 2017

Segment Reporting [Abstract]

Schedule of financial information by segment

Selected financial information by segment for the periods shown was as follows (intercompany transactions are eliminated in Corporate and eliminations):



	For the year ended December 31,			For the Transition Period ended December 31,			For the year ended May 31,
	2017			2016			2016			2015
Revenues
Services	$	543,565		$	293,218		$	553,279		$	540,224
International	144,265			104,013			143,025			146,953
Products and Systems	23,297			14,541			30,293			31,255
Corporate and eliminations	(10,157		)	(7,611		)	(7,416		)	(7,180		)
	$	700,970		$	404,161		$	719,181		$	711,252



	For the year ended December 31,			For the Transition Period ended December 31,		For the year ended May 31,
	2017			2016		2016		2015
Gross profit
Services	$	139,160		$	75,784	$	145,262	$	135,201
International	38,974			34,210		43,613		34,572
Products and Systems	9,798			6,920		14,022		14,314
Corporate and eliminations	(220		)	90		111		646
	$	187,712		$	117,004	$	203,008	$	184,733



	For the year ended December 31,			For the Transition Period ended December 31,			For the year ended May 31,
	2017			2016			2016			2015
Income from operations
Services	$	46,677		$	22,411		$	52,552		$	49,142
International	3,537			10,597			9,293			(575		)
Products and Systems	(16,991		)	(254		)	2,688			2,461
Corporate and eliminations	(29,063		)	(15,221		)	(21,356		)	(20,675		)
	$	4,160		$	17,533		$	43,177		$	30,353



	For the year ended December 31,			For the Transition Period ended December 31,			For the year ended May 31,
	2017			2016			2016			2015
Depreciation and amortization
Services	$	21,649		$	12,765		$	22,725		$	22,268
International	7,768			5,306			7,774			8,451
Products and Systems	2,180			1,372			2,323			2,426
Corporate and eliminations	(214		)	(244		)	(348		)	141
	$	31,383		$	19,199		$	32,474		$	33,286



	December 31,
	2017		2016
Intangible assets, net
Services	$	46,864	$	19,550
International	13,899		14,139
Products and Systems	2,261		5,482
Corporate and eliminations	715		836
	$	63,739	$	40,007



	December 31,
	2017		2016
Total assets
Services	$	377,585	$	291,539
International	150,779		130,427
Products and Systems	12,733		28,964
Corporate and eliminations	13,344		18,497
	$	554,441	$	469,427

Schedule of revenue and long-lived assets by geographic area

Revenue and long-lived assets by geographic area was as follows:



	For the year ended December 31,		For the Transition Period ended December 31,		For the year ended May 31,
	2017		2016		2016		2015
Revenue
United States	$	466,683	$	256,926	$	519,361	$	491,818
Other Americas	86,870		41,777		67,809		68,628
Europe	132,421		91,847		118,566		137,071
Asia-Pacific	14,996		13,611		13,445		13,735
	$	700,970	$	404,161	$	719,181	$	711,252



	December 31,
	2017		2016
Long-lived assets
United States	$	237,616	$	186,960
Other Americas	36,011		29,065
Europe	80,693		67,072
	$	354,320	$	283,097

Twelve Months Ended December 31, 2016 and Seven Months Ended December 31, 2015 Comparative Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2017

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Condensed Consolidated of Income for the Twelve Months Ended December 31, 2016 and Seven Months ended December 31, 2015

The condensed consolidated statement of income for the twelve months ended December 31, 2016 and the seven months ended December 31, 2015 is as follows:



	Twelve Months Ended December 31, 2016			Seven Months Ended December 31, 2015
	(unaudited)
Revenues	$	684,762		$	427,913
Cost of revenues	468,929			292,718
Depreciation	21,699			12,005
Gross profit	194,134			123,190
Selling, general and administrative expenses	148,914			81,117
Research and engineering	2,670			1,431
Depreciation and amortization	10,689			6,503
Litigation charges	6,320			—
Acquisition-related benefit, net	(5		)	(959		)
Income from operations	25,546			35,098
Interest expense, net	3,075			3,672
Income before provision for income taxes	22,471			31,426
Provision for income taxes	8,008			11,627
Net income	14,463			19,799
Less: Net income (loss) attributable to non-controlling interests	54			(15		)
Net income available to Mistras Group, Inc. shareholders	$	14,409		$	19,814
Net income per share: Basic	$	0.50		$	0.69
Net income per share: Diluted	$	0.48		$	0.67
Weighted average shares outstanding:
Basic	28,960			28,810
Diluted	30,114			29,676

Selected Quarterly Financial Information (unaudited) (Tables)

12 Months Ended

Dec. 31, 2017

Quarterly Financial Information Disclosure [Abstract]

Summary of the quarterly results of operations

The following is a summary of the quarterly results of operations for calendar years 2017 and 2016.



Fiscal quarter ended	December 31, 2017		September 30, 2017			June 30, 2017		March 31, 2017
Revenues	$	187,643	$	179,570		$	170,439	$	163,318
Gross Profit	50,319		47,897			46,343		43,153
Income (loss) from operations	6,282		(10,375		)	5,003		3,250
Net income (loss) attributable to Mistras Group, Inc.	$	884	$	(6,968	)	$	2,217	$	1,692
Earnings (loss) per common share:
Basic	$	0.03	$	(0.25	)	$	0.08	$	0.06
Diluted	$	0.03	$	(0.25	)	$	0.07	$	0.06



Fiscal quarter ended	December 31, 2016		September 30, 2016		June 30, 2016		March 31, 2016
Revenues	$	170,156	$	168,811	$	178,340	$	167,455
Gross Profit	47,978		50,651		51,535		43,970
Income from operations	2,944		12,116		4,840		5,646
Net income attributable to Mistras Group, Inc.	$	963	$	7,238	$	2,761	$	3,447
Earnings per common share:
Basic	$	0.03	$	0.25	$	0.10	$	0.12
Diluted	$	0.03	$	0.24	$	0.09	$	0.11

Description of Business and Basis of Presentation (Details) - International	7 Months Ended	12 Months Ended
	Dec. 31, 2016 mo	May 31, 2015 subsidiary
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Difference of period between the consolidation of International segment subsidiaries	1 month
Number of months less than the actual number of months from the acquisition date for which results of international segment subsidiaries are included in consolidation \| mo	1
Disposal of Foreign Subsidiaries \| Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of additional subsidiaries for sale \| subsidiary		2

Summary of Significant Accounting Policies - Narrative (Details)	3 Months Ended		7 Months Ended	12 Months Ended
	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Dec. 31, 2016 USD ($) customer	Dec. 31, 2017 USD ($) customer	Dec. 31, 2016	May 31, 2016 USD ($) customer	May 31, 2015 USD ($) customer
Concentration of Credit Risk
Goodwill impairment charge	$ 0			$ 13,197,000
Foreign currency (gains) and losses				600,000
Minimum amount of of excess self-insurance claims paid to reduce exposure				300,000
Selling, General and Administrative Expenses
Concentration of Credit Risk
Advertising expense			$ 1,200,000	$ 1,900,000		$ 1,800,000	$ 2,200,000
Foreign currency (gains) and losses			$ (700,000)			$ (100,000)	$ 1,500,000
Software/Technology
Concentration of Credit Risk
Estimated useful life of software				3 years
Products and Systems
Concentration of Credit Risk
Goodwill impairment charge		$ 13,200,000		$ 13,197,000
Impairment charge of long-lived assets		$ 2,600,000
Products and Systems \| Software/Technology
Concentration of Credit Risk
Impairment charge of long-lived assets				$ 2,400,000
Customer concentration risk \| Revenues
Concentration of Credit Risk
Number of customers \| customer			1	1		1	0
Percentage of concentration risk				11.00%	12.00%	10.00%	10.00%
Customer concentration risk \| Accounts Receivable
Concentration of Credit Risk
Number of customers \| customer			1	1
Percentage of concentration risk			11.00%	7.00%

Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								7 Months Ended		12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	May 31, 2016	May 31, 2015
Basic (loss) earnings per share
Net (loss) income attributable to Mistras Group, Inc.	$ 884	$ (6,968)	$ 2,217	$ 1,692	$ 963	$ 7,238	$ 2,761	$ 3,447	$ 9,568	$ 19,814	$ (2,175)	$ 14,409	$ 24,654	$ 16,081
Denominator
Weighted average common shares outstanding (in shares)									28,989	28,810	28,422	28,960	28,856	28,613
Basic (loss) earnings per share (in dollars per share)	$ 0.03	$ (0.25)	$ 0.08	$ 0.06	$ 0.03	$ 0.25	$ 0.10	$ 0.12	$ 0.33	$ 0.69	$ (0.08)	$ 0.50	$ 0.85	$ 0.56
Denominator
Weighted average common shares outstanding (in shares)									28,989	28,810	28,422	28,960	28,856	28,613
Dilutive effect of stock options outstanding (in shares)									791				712	719
Dilutive effect of restricted stock units outstanding (in shares)									345				323	258
Weighted average common shares outstanding, diluted (in shares)									30,125	29,676	28,422	30,114	29,891	29,590
Diluted (loss) earnings per share (in dollars per share)	$ 0.03	$ (0.25)	$ 0.07	$ 0.06	$ 0.03	$ 0.24	$ 0.09	$ 0.11	$ 0.32	$ 0.67	$ (0.08)	$ 0.48	$ 0.82	$ 0.54

Earnings per Share - Potential Common Shares Excluded From Computation of Diluted Earnings (Details) - shares shares in Thousands	7 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2017	May 31, 2016	May 31, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common stock excluded from computation of earnings per share (in shares)	2	1,163	29	7
Stock Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common stock excluded from computation of earnings per share (in shares)	0	810	5	6
Potential common stock excluded from computation of diluted earnings per share due to net loss for the period (in shares)		805
RSUs and PSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common stock excluded from computation of earnings per share (in shares)	2	353	24	1
Potential common stock excluded from computation of diluted earnings per share due to net loss for the period (in shares)		351

Accounts Receivable, net (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Receivables [Abstract]
Trade accounts receivable	$ 141,952	$ 133,704
Allowance for doubtful accounts	(3,872)	(2,852)
Accounts receivable, net	138,080	130,852
Accrued unbilled revenues	$ 14,400	$ 16,800

Inventories (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Inventory Disclosure [Abstract]
Raw materials	$ 5,105	$ 5,054
Work in progress	1,192	1,246
Finished goods	2,746	2,335
Services-related consumable supplies	1,460	1,382
Inventory	$ 10,503	$ 10,017

Property, Plant and Equipment, net (Details) - USD ($) $ in Thousands	7 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2017	May 31, 2016	May 31, 2015
Property, Plant and Equipment, net
Property, plant and equipment, gross	$ 199,972	$ 232,368
Accumulated depreciation and amortization	(126,823)	(145,225)
Property, plant and equipment, net	73,149	87,143
Depreciation expense	14,000	22,400	$ 22,900	$ 22,200
Land
Property, Plant and Equipment, net
Property, plant and equipment, gross	1,714	2,414
Building and improvements
Property, Plant and Equipment, net
Property, plant and equipment, gross	19,261	$ 24,003
Building and improvements \| Minimum
Property, Plant and Equipment, net
Useful Life		30 years
Building and improvements \| Maximum
Property, Plant and Equipment, net
Useful Life		40 years
Office furniture and equipment
Property, Plant and Equipment, net
Property, plant and equipment, gross	9,069	$ 14,230
Office furniture and equipment \| Minimum
Property, Plant and Equipment, net
Useful Life		5 years
Office furniture and equipment \| Maximum
Property, Plant and Equipment, net
Useful Life		8 years
Machinery and equipment
Property, Plant and Equipment, net
Property, plant and equipment, gross	$ 169,928	$ 191,721
Machinery and equipment \| Minimum
Property, Plant and Equipment, net
Useful Life		5 years
Machinery and equipment \| Maximum
Property, Plant and Equipment, net
Useful Life		7 years

Acquisitions and Dispositions - Acquisitions Narrative (Details) $ in Thousands	7 Months Ended	12 Months Ended
	Dec. 31, 2016 USD ($) entity	Dec. 31, 2017 USD ($) entity	May 31, 2016 USD ($)
Business Acquisition [Line Items]
Period over which potential acquisition-related contingent consideration would be payable		2 years 6 months
Goodwill	$ 169,940	$ 203,438	$ 169,220
Revenue for the period subsequent to closing of the transaction		17,900
Aggregate income from operation for the period subsequent to closing of transaction		800
Acquisition-related expense		$ 900
Minimum
Business Acquisition [Line Items]
Amortization period of intangible assets acquired		2 years
Maximum
Business Acquisition [Line Items]
Amortization period of intangible assets acquired		14 years
Acquisitions in Fiscal 2017
Business Acquisition [Line Items]
Number of entities acquired \| entity		3
Cash consideration paid		$ 83,963
Contingent consideration liability		3,407
Working capital adjustments		150
Notes payable assumed		0
Goodwill		41,695
Goodwill deductible for tax purposes		39,700
Finite-lived intangible assets acquired		31,671
Acquisitions in Fiscal 2017 \| Customer Relationships and Noncompete Agreements
Business Acquisition [Line Items]
Finite-lived intangible assets acquired		$ 31,700
Acquisitions in Fiscal 2017 \| Canada
Business Acquisition [Line Items]
Number of entities acquired \| entity		1
Acquisitions in Fiscal 2017 \| Canada and U.S.
Business Acquisition [Line Items]
Percentage of equity interest acquired		100.00%
Cash consideration paid		$ 79,500
Contingent consideration liability		$ 2,400
Contingent consideration initial payment period		3 years
Working capital adjustments		$ 200
Acquisitions in Fiscal 2017 \| U.S.
Business Acquisition [Line Items]
Number of entities acquired \| entity		1
Cash consideration paid		$ 4,500
Contingent consideration liability		$ 3,500
Contingent consideration initial payment period		3 years
Acquisitions in Transition Period
Business Acquisition [Line Items]
Number of entities acquired \| entity	3
Cash consideration paid	$ 8,295
Contingent consideration liability	1,630
Working capital adjustments	0
Notes payable assumed	325
Goodwill	4,120	$ 41,700
Finite-lived intangible assets acquired	$ 3,367
Acquisitions in Transition Period \| Canada
Business Acquisition [Line Items]
Number of entities acquired \| entity	2
Percentage of equity interest acquired	100.00%
Cash consideration paid	$ 1,300
Contingent consideration liability	600
Notes payable assumed	$ 300
Period over which potential acquisition-related contingent consideration would be payable	3 years
Acquisitions in Transition Period \| U.S.
Business Acquisition [Line Items]
Number of entities acquired \| entity	1
Cash consideration paid	$ 7,000
Contingent consideration liability	$ 2,000
Period over which potential acquisition-related contingent consideration would be payable	3 years

Acquisitions and Dispositions - Estimated Fair Value of the Assets Acquired and Liabilities Assumed (Details) $ in Thousands	7 Months Ended	12 Months Ended
	Dec. 31, 2016 USD ($) entity	Dec. 31, 2017 USD ($) entity	May 31, 2016 USD ($)
Estimated fair value of the assets acquired and liabilities assumed
Goodwill	$ 169,940	$ 203,438	$ 169,220
Acquisitions in Fiscal 2017
Acquisitions
Number of entities \| entity		3
Consideration transferred:
Cash paid		$ 83,963
Working capital adjustments		150
Notes payable		0
Contingent consideration		3,407
Consideration paid		87,520
Estimated fair value of the assets acquired and liabilities assumed
Current net assets		7,165
Debt and other long-term liabilities		(2,848)
Property, plant and equipment		11,115
Deferred tax asset (liability)		(1,278)
Intangibles		31,671
Goodwill		41,695
Net assets acquired		87,520
Acquisitions in Transition Period
Acquisitions
Number of entities \| entity	3
Consideration transferred:
Cash paid	$ 8,295
Working capital adjustments	0
Notes payable	325
Contingent consideration	1,630
Consideration paid	10,250
Estimated fair value of the assets acquired and liabilities assumed
Current net assets	1,632
Debt and other long-term liabilities	(214)
Property, plant and equipment	953
Deferred tax asset (liability)	392
Intangibles	3,367
Goodwill	4,120	$ 41,700
Net assets acquired	$ 10,250

Acquisitions and Dispositions - Dispositions Narrative (Details) $ in Thousands		3 Months Ended	7 Months Ended	12 Months Ended
	May 22, 2015 USD ($) subsidiary	Dec. 31, 2017 subsidiary	Dec. 31, 2016 USD ($)	Dec. 31, 2017 USD ($)	May 31, 2016 USD ($)	May 31, 2015 USD ($) subsidiary
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Losses associated with the exit of foreign operations			$ 0	$ 0	$ 0	$ 2,516
Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations \| Disposal of Foreign Subsidiaries
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of foreign subsidiaries sold and held-for-sale \| subsidiary						3
Disposal group, percentage of assets to consolidated assets						0.60%
Disposal group, percentage of liabilities to consolidated liabilities						0.30%
Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations \| Disposal of Foreign Subsidiaries \| Products and Systems
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairment charges on subsidiaries held-for-sale				$ 2,600
Disposal group, percentage of assets to consolidated assets		0.40%		0.40%
Disposal group, percentage of liabilities to consolidated liabilities		0.20%		0.20%
Number of subsidiaries classified as held for sale \| subsidiary		1
Disposal group, percentage of consolidated revenues				0.60%
Disposal group, loss from operations				$ 3,500
Russia \| Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations \| Disposal of Foreign Subsidiaries
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of subsidiaries sold \| subsidiary	1
Losses associated with the exit of foreign operations	$ 400
Russia and Japan \| Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations \| Disposal of Foreign Subsidiaries
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Losses associated with the exit of foreign operations						$ 2,500
Impairment charges on subsidiaries held-for-sale						$ 2,100

Acquisitions and Dispositions - Acquisition-Related Expense (Details) - USD ($) $ in Thousands	7 Months Ended		12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	May 31, 2016	May 31, 2015
Business Acquisition [Line Items]
Adjustments to fair value of contingent consideration liabilities	$ 262		$ (463)		$ (2,066)	$ (5,382)
Acquisition-related (benefit) expense, net	496	$ (959)	482	$ (5)	(1,453)	(5,167)
Acquisitions in Fiscal 2017
Business Acquisition [Line Items]
Due diligence, professional fees and other transaction costs			945
Adjustments to fair value of contingent consideration liabilities			(463)
Acquisition-related (benefit) expense, net			$ 482
Acquisitions in Transition Period
Business Acquisition [Line Items]
Due diligence, professional fees and other transaction costs	231
Adjustments to fair value of contingent consideration liabilities	265
Acquisition-related (benefit) expense, net	$ 496
Acquisitions in Fiscal 2016
Business Acquisition [Line Items]
Due diligence, professional fees and other transaction costs					629
Adjustments to fair value of contingent consideration liabilities					(2,082)
Acquisition-related (benefit) expense, net					$ (1,453)
Acquisitions in Fiscal 2015
Business Acquisition [Line Items]
Due diligence, professional fees and other transaction costs						215
Adjustments to fair value of contingent consideration liabilities						(5,382)
Acquisition-related (benefit) expense, net						$ (5,167)

Goodwill (Details) - USD ($)	3 Months Ended		7 Months Ended	12 Months Ended
Goodwill (Details) - USD ($)	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016	Dec. 31, 2017
Changes in the carrying amount of goodwill
Balance at the beginning of the period			$ 169,220,000	$ 169,940,000
Goodwill acquired during the year			4,120,000	41,695,000
Impairment charge	$ 0			(13,197,000)
Adjustments to preliminary purchase price allocations			(19,000)	(211,000)
Foreign currency translation			(3,381,000)	5,211,000
Balance at the end of the period	203,438,000		169,940,000	203,438,000
Services
Changes in the carrying amount of goodwill
Balance at the beginning of the period			119,683,000	123,392,000
Goodwill acquired during the year			4,120,000	41,695,000
Impairment charge				0
Adjustments to preliminary purchase price allocations			(19,000)	(211,000)
Foreign currency translation			(392,000)	925,000
Balance at the end of the period	165,801,000		123,392,000	165,801,000
International
Changes in the carrying amount of goodwill
Balance at the beginning of the period			36,340,000	33,351,000
Goodwill acquired during the year			0	0
Impairment charge				0
Adjustments to preliminary purchase price allocations			0	0
Foreign currency translation			(2,989,000)	4,286,000
Balance at the end of the period	37,637,000		33,351,000	37,637,000
Products and Systems
Changes in the carrying amount of goodwill
Balance at the beginning of the period			13,197,000	13,197,000
Goodwill acquired during the year			0	0
Impairment charge		$ (13,200,000)		(13,197,000)
Adjustments to preliminary purchase price allocations			0	0
Foreign currency translation			0	0
Balance at the end of the period	$ 0		$ 13,197,000	$ 0

Goodwill - Narrative (Details) - USD ($)	3 Months Ended		12 Months Ended
Goodwill - Narrative (Details) - USD ($)	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Goodwill
Goodwill impairment charge	$ 0		$ 13,197,000
Goodwill, cumulative impairment	23,100,000		23,100,000
Products and Systems
Goodwill
Goodwill impairment charge		$ 13,200,000	13,197,000
Goodwill, cumulative impairment	13,200,000		13,200,000
International
Goodwill
Goodwill impairment charge			0
Goodwill, cumulative impairment	$ 9,900,000		$ 9,900,000	$ 9,900,000

Intangible Assets - Gross Carrying Amount and Accumulated Amortization (Details) - USD ($) $ in Thousands	7 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2017	May 31, 2016	May 31, 2015
Finite-Lived Intangible Assets [Line Items]
Gross Amount	$ 118,096	$ 155,441
Accumulated Amortization	(78,089)	(89,089)
Impairment		(2,613)
Net Carrying Amount	40,007	63,739
Amortization expense	5,200	9,000	$ 9,600	$ 11,100
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Gross Amount	81,559	113,299
Accumulated Amortization	(50,417)	(58,107)
Impairment		(170)
Net Carrying Amount	31,142	$ 55,022
Customer relationships \| Minimum
Finite-Lived Intangible Assets [Line Items]
Useful Life (Years)		5 years
Customer relationships \| Maximum
Finite-Lived Intangible Assets [Line Items]
Useful Life (Years)		14 years
Software/Technology
Finite-Lived Intangible Assets [Line Items]
Useful Life (Years)		3 years
Gross Amount	18,128	$ 19,523
Accumulated Amortization	(12,577)	(14,133)
Impairment		(2,411)
Net Carrying Amount	5,551	2,979
Amortization expense	500	$ 700	$ 1,000	$ 900
Software/Technology \| Minimum
Finite-Lived Intangible Assets [Line Items]
Useful Life (Years)		3 years
Software/Technology \| Maximum
Finite-Lived Intangible Assets [Line Items]
Useful Life (Years)		15 years
Covenants not to compete
Finite-Lived Intangible Assets [Line Items]
Gross Amount	11,143	$ 12,510
Accumulated Amortization	(9,647)	(10,438)
Impairment		0
Net Carrying Amount	1,496	$ 2,072
Covenants not to compete \| Minimum
Finite-Lived Intangible Assets [Line Items]
Useful Life (Years)		2 years
Covenants not to compete \| Maximum
Finite-Lived Intangible Assets [Line Items]
Useful Life (Years)		5 years
Other
Finite-Lived Intangible Assets [Line Items]
Gross Amount	7,266	$ 10,109
Accumulated Amortization	(5,448)	(6,411)
Impairment		(32)
Net Carrying Amount	$ 1,818	$ 3,666
Other \| Minimum
Finite-Lived Intangible Assets [Line Items]
Useful Life (Years)		2 years
Other \| Maximum
Finite-Lived Intangible Assets [Line Items]
Useful Life (Years)		5 years

Intangible Assets - Narrative (Details) - Products and Systems - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Impairment of finite-lived intangible assets	$ 2.6
Software/Technology
Finite-Lived Intangible Assets [Line Items]
Impairment of finite-lived intangible assets		$ 2.4
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Impairment of finite-lived intangible assets		0.2
Other
Finite-Lived Intangible Assets [Line Items]
Impairment of finite-lived intangible assets		$ 0.1

Intangible Assets - Expected Amortization Expense (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
2018	$ 10,117
2019	8,952
2020	7,483
2021	6,411
2022	6,076
Thereafter	24,700
Net Carrying Amount	$ 63,739	$ 40,007

Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Payables and Accruals [Abstract]
Accrued salaries, wages and related employee benefits	$ 27,185	$ 23,442
Contingent consideration	3,430	1,826
Accrued workers' compensation and health benefits	5,181	6,351
Deferred revenues	6,338	3,743
Legal settlement accrual	1,600	6,320
Other accrued expenses	21,827	17,015
Total accrued expenses and other current liabilities	$ 65,561	$ 58,697

- Definition

The carrying amount of consideration received or receivable as of the balance sheet date on potential earnings that were not recognized as revenue in conformity with GAAP, and which are expected to be recognized as such within one year or the normal operating cycle, if longer, including sales, license fees, and royalties, but excluding interest income.

+ References + Details

Long-Term Debt - Schedule of Long-Term Debt (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Total debt	$ 166,878	$ 87,296
Less: Current portion	(2,358)	(1,379)
Long-term debt, net of current portion	164,520	85,917
Senior credit facility
Debt Instrument [Line Items]
Total debt	156,948	82,776
Notes payable
Debt Instrument [Line Items]
Total debt	228	320
Other
Debt Instrument [Line Items]
Total debt	$ 9,702	$ 4,200

Long-Term Debt - Narrative (Details)		12 Months Ended
Long-Term Debt - Narrative (Details)	Dec. 08, 2017 USD ($) quarter	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Oct. 30, 2014 USD ($)
Long-Term Debt
Other debt outstanding		$ 166,878,000	$ 87,296,000
Senior credit facility
Long-Term Debt
Maximum borrowing capacity	$ 250,000,000.0			$ 175,000,000.0
Higher borrowing capacity option	300,000,000.0
Maximum borrowing capacity in non-U.S. Dollar currencies	30,000,000.0
Maximum amount available for the issuance of letters of credit	10,000,000.0
Long-term line of credit		156,900,000
Outstanding letters of credit		4,900,000
Capitalized debt modification costs		800,000
Non-recurring charges threshold used for calculation of Funded Debt Leverage Ratio	$ 5,000,000
Number of consecutive fiscal quarters used for calculating Funded Debt Leverage Ratio \| quarter	4
Funded Debt Leverage Ratio at which the entity will bear the maximum interest rate margin	2.75
Additional interest rate margin if Funded Debt Leverage Ratio exceeds threshold (as a percent)	2.00%
Preceding period used for calculating Interest Coverage Ratio	12 months
Number of quarters for temporarily increase in Funded Debt Leverage ratio following business acquisitions \| quarter	4
Other debt outstanding		$ 156,948,000	82,776,000
Senior credit facility \| Minimum
Long-Term Debt
Interest coverage ratio	3.0
Senior credit facility \| Maximum
Long-Term Debt
Funded Debt Leverage Ratio at which the entity will have the benefit of lowest interest margin	0.5
Funded Debt Leverage Ratio for additional interest payment	3.5
Funded Debt Leverage Ratio temporarily increase due to business acquisitions	3.75
Senior credit facility \| LIBOR
Long-Term Debt
Reference rate, description	LIBOR
Senior credit facility \| LIBOR \| Minimum
Long-Term Debt
Margin rate (as a percent)	1.00%
Senior credit facility \| LIBOR \| Maximum
Long-Term Debt
Margin rate (as a percent)	2.00%
Senior credit facility \| Base rate
Long-Term Debt
Reference rate, description	base rate
Senior credit facility \| Base rate \| Minimum
Long-Term Debt
Margin rate (as a percent)	(1.25%)
Senior credit facility \| Base rate \| Maximum
Long-Term Debt
Margin rate (as a percent)	(0.375%)
Notes payable
Long-Term Debt
Maturity term from the date of acquisition		3 years
Interest rate, minimum (as a percent)		3.20%
Other debt outstanding		$ 228,000	320,000
Other
Long-Term Debt
Other debt outstanding		$ 9,702,000	$ 4,200,000
Other \| Minimum
Long-Term Debt
Interest rate, minimum (as a percent)		0.60%
Monthly debt payments		$ 1,000
Other \| Maximum
Long-Term Debt
Interest rate, minimum (as a percent)		6.20%
Monthly debt payments		$ 18,000

Long-Term Debt - Scheduled Principal Payments (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Debt Disclosure [Abstract]
2018	$ 2,358
2019	1,664
2020	1,243
2021	892
2022	157,728
Thereafter	2,993
Total debt	$ 166,878	$ 87,296

Fair Value Measurements (Details) - USD ($) $ in Thousands	7 Months Ended	12 Months Ended
Fair Value Measurements (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2017	May 31, 2016	May 31, 2015
Contingent Consideration Liability [Roll Forward]
Revaluation	$ (262)	$ 463	$ 2,066	$ 5,382
Level 3
Contingent Consideration Liability [Roll Forward]
Contingent consideration, beginning balance	2,075	3,094
Acquisitions	1,630	3,407
Payments	(795)	(560)
Accretion of liability	136	272
Revaluation	126	(735)
Foreign currency translation	(78)	30
Contingent consideration, ending balance	$ 3,094	$ 5,508	$ 2,075

Share-Based Compensation - Additional Information (Details)	12 Months Ended
	Dec. 31, 2017 plan shares	Dec. 31, 2016 shares	May 31, 2016 shares	May 31, 2015 shares	May 31, 2014 shares
Share-based compensation
Number of employee stock ownership plans \| plan	3
Stock options outstanding (in shares)	2,130,000	2,167,000	2,232,000	2,287,000	2,352,000
Restricted Stock Unit Awards
Share-based compensation
Unvested restricted stock units outstanding (in shares)	532,000	569,000	575,000	564,000	628,000
2007 and 2009 Plans
Share-based compensation
Number of awards authorized for grants (in shares)	0
2007 and 2009 Plans \| Stock Options
Share-based compensation
Stock options outstanding (in shares)	2,130,000
2007 and 2009 Plans \| Restricted Stock Unit Awards
Share-based compensation
Unvested restricted stock units outstanding (in shares)	724,000
2016 Plan
Share-based compensation
Number of awards authorized for grants (in shares)	1,700,000
Number of awards available for future grants (in shares)	1,438,000

Share-Based Compensation - Stock Options Narrative (Details) - USD ($)	7 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2017	May 31, 2016	May 31, 2015
Share-based compensation
Stock options granted (in shares)	0	0	0	0
Unrecognized compensation costs related to stock options		$ 0
Stock Options
Share-based compensation
Recognized share-based compensation expense	$ 0	$ 0	$ 100,000	$ 100,000
Stock options granted (in shares)	0		0	0

Share-Based Compensation - Cash Proceeds and Intrinsic Value of Stock Options Exercised (Details) - USD ($) $ in Thousands	7 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2017	May 31, 2016	May 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Cash proceeds from options exercised	$ 604	$ 275	$ 543	$ 750
Aggregate intrinsic value of options exercised	$ 993	$ 580	$ 658	$ 563

Share-Based Compensation - Stock Option Activity (Details) - $ / shares	7 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2017	May 31, 2016	May 31, 2015
Common Stock Options (shares)
Outstanding at beginning of year: (in shares)	2,232,000	2,167,000	2,287,000	2,352,000
Granted (in shares)	0	0	0	0
Exercised (in shares)	(65,000)	(37,000)	(55,000)	(65,000)
Expired or forfeited (in shares)	0	0	0	0
Outstanding at end of year: (in shares)	2,167,000	2,130,000	2,232,000	2,287,000
Weighted Average Exercise Price (in dollar per share)
Outstanding at beginning of year: (in dollars per share)	$ 13.21	$ 13.33	$ 13.13	$ 13.09
Granted (in dollars per share)	0.00	0.00	0.00	0.00
Exercised (in dollars per share)	9.27	7.39	9.87	11.54
Expired or forfeited (in dollars per share)	0.00	0.00	0.00	0.00
Outstanding at end of year: (in dollars per share)	$ 13.33	$ 13.43	$ 13.21	$ 13.13

Share-Based Compensation - Stock Options Outstanding and Exercisable (Details) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) $ / shares shares
Options Outstanding
Total Options Outstanding (in shares) \| shares	2,130
Options Exercisable
Number Exercisable (in shares) \| shares	2,130
Aggregate Intrinsic Value
Options Outstanding (in dollars) \| $	$ 21,374
Options Exercisable (in dollars) \| $	$ 21,374
$10.00-$11.54
Options Outstanding
Total Options Outstanding (in shares) \| shares	35
Weighted Average Remaining Life (Years)	1 year 1 month 6 days
Weighted Average Exercise Price (in dollars per share)	$ 10.54
Options Exercisable
Number Exercisable (in shares) \| shares	35
Weighted Average Exercise Price (in dollars per share)	$ 10.54
Aggregate Intrinsic Value
Range of Exercise Prices, Lower Limit (in dollars per share)	10.00
Range of Exercise Prices, Upper Limit (in dollars per share)	$ 11.54
$13.46-$22.35
Options Outstanding
Total Options Outstanding (in shares) \| shares	2,095
Weighted Average Remaining Life (Years)	1 year 8 months 12 days
Weighted Average Exercise Price (in dollars per share)	$ 13.48
Options Exercisable
Number Exercisable (in shares) \| shares	2,095
Weighted Average Exercise Price (in dollars per share)	$ 13.48
Aggregate Intrinsic Value
Range of Exercise Prices, Lower Limit (in dollars per share)	13.46
Range of Exercise Prices, Upper Limit (in dollars per share)	$ 22.35

Share-Based Compensation - Restricted Stock Units Awards Narrative (Details) shares in Thousands, $ in Millions	7 Months Ended	12 Months Ended
	Dec. 31, 2016 USD ($) director shares	Dec. 31, 2017 USD ($) director shares	May 31, 2016 USD ($) director shares	May 31, 2015 USD ($) director shares
Non-employee directors
Share-based compensation
Number of non-employee directors to whom fully vested common stock is granted \| director				5
Restricted Stock Unit Awards
Share-based compensation
Recognized share-based compensation expense \| $	$ 2.6	$ 4.5	$ 4.4	$ 4.7
Unrecognized compensation cost, net of estimated forfeitures, related to restricted stock unit awards \| $		$ 8.2
Weighted-average period over which unrecognized compensation cost is expected to be recognized		2 years 3 months 3 days
Number of restricted stocks vested (in shares) \| shares	207	185	223	232
Number of restricted stocks units granted (in shares) \| shares	219	183	264	192
Fair value of shares vested \| $	$ 5.1	$ 3.4	$ 3.5	$ 5.2
Restricted Stock Unit Awards \| Non-employee directors
Share-based compensation
Number of restricted stocks units granted (in shares) \| shares	10	21
Fair value of shares vested \| $	$ 0.3	$ 0.4	$ 0.5	$ 0.4
Number of fully vested common stock granted (in shares) \| shares			28	21
Number of non-employee directors to whom fully vested common stock is granted \| director	5	5	5

Share-Based Compensation - Restricted Stock Awards Outstanding (Details) - Restricted Stock Unit Awards - $ / shares shares in Thousands	7 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2017	May 31, 2016	May 31, 2015	May 31, 2014
Units
Outstanding at beginning of period: (in shares)	575	569	564	628
Granted (in shares)	219	183	264	192
Released (in shares)	(207)	(185)	(223)	(232)
Forfeited (in shares)	(18)	(35)	(30)	(24)
Outstanding at end of period: (in shares)	569	532	575	564
Weighted Average Grant-Date Fair Value
Outstanding at beginning of period: (in dollars per share)	$ 20.81	$ 21.05	$ 18.85	$ 20.47	$ 19.37
Granted (in dollars per share)	24.48	21.26	16.73	21.87
Released (in dollars per share)	19.40	20.49	20.40	18.17
Forfeited (in dollars per share)	19.55	21.45	19.26	20.57
Outstanding at end of period: (in dollars per share)	$ 20.81	$ 21.05	$ 18.85	$ 20.47	$ 19.37

Share-Based Compensation - Performance Restricted Stock Units Narrative (Details) - USD ($) shares in Thousands, $ in Millions	3 Months Ended		7 Months Ended	12 Months Ended
	Mar. 31, 2017	Aug. 31, 2015	Dec. 31, 2016	Dec. 31, 2017	May 31, 2016	May 31, 2015	May 31, 2014
PRSUs
Share-based compensation
Number of restricted stocks units granted (in shares)			105	128
Unvested restricted stock units outstanding (in shares)			290	278	328
PRSUs \| Executive and senior officers
Share-based compensation
Unvested restricted stock units outstanding (in shares)				278
Recognized share-based compensation expense			$ 1.7	$ 1.7	$ 1.6	$ 1.5
Unrecognized compensation cost, net of estimated forfeitures, related to restricted stock unit awards				$ 2.3
Weighted-average period over which unrecognized compensation cost is expected to be recognized				2 years
Income tax benefit recognized on share-based compensation			1.6	$ 2.2	$ 2.2	$ 2.3
PRSUs \| Fiscal 2014 Grants \| Executive and senior officers
Share-based compensation
Requisite service period							3 years
PRSUs \| Fiscal 2015 Grants \| Executive and senior officers
Share-based compensation
Requisite service period						3 years
PRSUs \| Fiscal 2016 Grants \| Executive and senior officers
Share-based compensation
Requisite service period					5 years
Number of fully vested common stock granted (in shares)		154
Increase in number of shares authorized for grant (in shares)					104
Number of awards authorized for grants (in shares)					258
PRSUs \| Transition Period 2016 Grants \| Accrued Expenses and Other Current Liabilities
Share-based compensation
Aggregate liability related to performance shares outstanding			$ 0.1
PRSUs \| Transition Period 2016 Grants \| Executive and senior officers
Share-based compensation
Number of restricted stocks units granted (in shares)			105
Reduction in number of shares authorized for grant (in shares)	3		73
Unvested restricted stock units outstanding (in shares)			12
PRSUs \| Fiscal 2017 Grants \| Accrued Expenses and Other Current Liabilities
Share-based compensation
Aggregate liability related to performance shares outstanding				$ 0.1
PRSUs \| Fiscal 2017 Grants \| Executive and senior officers
Share-based compensation
Number of restricted stocks units granted (in shares)				128
Reduction in number of shares authorized for grant (in shares)				65
Unvested restricted stock units outstanding (in shares)				13
PRSUs with one year performance condition \| Fiscal 2014 Grants \| Executive and senior officers
Share-based compensation
Award performance period							1 year
PRSUs with two year performance condition \| Fiscal 2014 Grants \| Executive and senior officers
Share-based compensation
Award performance period							2 years
PRSUs with three years performance condition \| Fiscal 2014 Grants \| Executive and senior officers
Share-based compensation
Award performance period							3 years
PRSUs with three years performance condition \| Fiscal 2015 Grants \| Executive and senior officers
Share-based compensation
Award performance period						3 years
PRSUs with three years performance condition \| Fiscal 2017 Grants \| Executive and senior officers
Share-based compensation
Payout performance period				1 year
Requisite service period				5 years
PRSUs with three years performance condition \| Fiscal 2017 Grants \| Executive and senior officers \| 1st Anniversary
Share-based compensation
Vesting period				4 years
PRSUs with three years performance condition \| Fiscal 2017 Grants \| Executive and senior officers \| 2nd Anniversary
Share-based compensation
Vesting period				2 years
PRSUs with three years performance condition \| Fiscal 2017 Grants \| Executive and senior officers \| 3rd Anniversary
Share-based compensation
Vesting period				3 years
PRSUs with three years performance condition \| Fiscal 2017 Grants \| Executive and senior officers \| 4th Anniversary
Share-based compensation
Vesting period				4 years
PRSUs with one year market condition \| Fiscal 2014 Grants \| Executive and senior officers
Share-based compensation
Award performance period			1 year				1 year
Payout for the fiscal 2014 market condition awards, percentage of target			170.00%
PRSUs with two year market condition \| Fiscal 2014 Grants \| Executive and senior officers
Share-based compensation
Award performance period			2 years				2 years
Payout for the fiscal 2014 market condition awards, percentage of target			105.00%
PRSUs with three years of performance and market conditions \| Fiscal 2014 Grants \| Executive and senior officers
Share-based compensation
Award performance period		3 years	3 years
PRSUs with three years of performance and market conditions \| Fiscal 2015 Grants \| Executive and senior officers
Share-based compensation
Award performance period		3 years

Share-Based Compensation - Performance Restricted Stock Units Activity (Details) - PRSUs - $ / shares shares in Thousands	7 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2017	May 31, 2016
Units
Outstanding at beginning of period: (in shares)	328	290
Granted (in shares)	105	128
Performance condition adjustments, net (in shares)	(54)	(68)
Released (in shares)	(89)	(72)
Forfeited (in shares)	0	0
Outstanding at end of period: (in shares)	290	278	328
Weighted Average Grant-Date Fair Value
Outstanding at beginning of period: (in dollars per share)	$ 16.01	$ 17.00	$ 17.02
Granted (in dollars per share)	24.90	20.42
Performance condition adjustments, net (in dollars per share)	24.49	20.55
Released (in dollars per share)	24.50	15.82
Forfeited (in dollars per share)	0.00	0.00
Outstanding at end of period: (in dollars per share)	$ 16.01	$ 17.00	$ 17.02

Income Taxes - Provision (Details) - USD ($) $ in Thousands	7 Months Ended		12 Months Ended
Income Taxes - Provision (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	May 31, 2016	May 31, 2015
(Loss) income before provision for income taxes from:
U.S. operations	$ 5,116		$ (7,303)		$ 27,772	$ 26,893
Foreign operations	10,365		7,077		10,643	(1,162)
(Loss) income before provision for income taxes	15,481	$ 31,426	(226)	$ 22,471	38,415	25,731
Current
Federal	1,990		3,558		9,156	8,489
States and local	483		39		1,537	1,177
Foreign	3,569		3,131		3,672	1,493
Reserve for uncertain tax positions	(39)		71		(529)	(48)
Total current	6,003		6,799		13,836	11,111
Deferred
Federal	6		(3,857)		82	(145)
States and local	(28)		(810)		(51)	(126)
Foreign	(514)		(437)		(557)	(2,416)
Total deferred	(536)		(5,104)		(526)	(2,687)
Net change in valuation allowance	403		247		455	1,316
Net deferred	(133)		(4,857)		(71)	(1,371)
Provision for income taxes	$ 5,870	$ 11,627	$ 1,942	$ 8,008	$ 13,765	$ 9,740

Income Taxes - Tax Rate Reconciliation (Details) - USD ($) $ in Thousands	7 Months Ended		12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	May 31, 2016	May 31, 2015
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Federal tax at statutory rate	$ 5,418		$ (79)		$ 13,445	$ 9,006
State taxes, net of federal benefit	296		(502)		966	683
Foreign tax	(573)		217		(610)	(517)
Contingent consideration	(4)		(63)		(425)	(914)
Permanent differences	373		377		245	196
Transition tax, net of foreign tax credits	0		3,942
Federal tax rate change due to the Tax Act	0		(1,956)
Other	(43)		(241)		(311)	(30)
Change in valuation allowance	403		247		455	1,316
Provision for income taxes	$ 5,870	$ 11,627	$ 1,942	$ 8,008	$ 13,765	$ 9,740
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Federal tax at statutory rate	35.00%		35.00%		35.00%	35.00%
State taxes, net of federal benefit	1.90%		221.60%		2.50%	2.70%
Foreign tax	(3.70%)		(95.80%)		(1.60%)	(2.00%)
Contingent consideration	0.00%		27.70%		(1.10%)	(3.60%)
Permanent differences	2.40%		(166.40%)		0.60%	0.80%
Transition tax, net of foreign tax credits	0.00%		(1741.40%)
Federal tax rate change due to the Tax Act	0.00%		864.00%
Other	(0.30%)		106.50%		(0.80%)	(0.10%)
Change in valuation allowance	2.60%		(109.10%)		1.20%	5.10%
Provision for income taxes	37.90%		(857.90%)		35.80%	37.90%

Income Taxes - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended								7 Months Ended		12 Months Ended
Income Taxes - Narrative (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	May 31, 2016	May 31, 2015
Operating Loss Carryforwards [Line Items]
Income tax expense									$ 5,870	$ 11,627	$ 1,942	$ 8,008	$ 13,765	$ 9,740
One-time benefit as result of remeasurement of federal deferred tax assets and liabilities											2,300
One-time expense due to imposition of transition tax											3,900
Incurred tax expense attributable to reduction in deferred tax assets											300
Deferred tax assets valuation allowance	$ 4,044				$ 3,896				3,896		4,044	3,896
Unrecognized tax benefits including penalties and interest, that would affect the effective tax rate, if recognized	200				300				300		200	300
Anticipated decrease in unrecognized tax benefits, excluding interest and penalties within the next 12 months	100										100
Net income (loss) of foreign subsidiaries	884	$ (6,968)	$ 2,217	$ 1,692	963	$ 7,238	$ 2,761	$ 3,447	9,568	$ 19,814	(2,175)	14,409	24,654	16,081
Federal
Operating Loss Carryforwards [Line Items]
Increase (decrease) in deferred tax assets valuation allowance											(100)
State
Operating Loss Carryforwards [Line Items]
Net operating losses	38,400										38,400
Increase (decrease) in deferred tax assets valuation allowance											200
Foreign
Operating Loss Carryforwards [Line Items]
Net operating losses	11,000										11,000
Net income (loss) of foreign subsidiaries									6,900		4,100		$ 7,500	$ (800)
Foreign \| Expiration Period 2021-2036
Operating Loss Carryforwards [Line Items]
Net operating losses	700										700
State and Foreign
Operating Loss Carryforwards [Line Items]
Increase (decrease) in deferred tax assets valuation allowance											100
State and Foreign \| Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations \| Disposal of Foreign Subsidiaries
Operating Loss Carryforwards [Line Items]
Deferred tax assets valuation allowance	4,000				$ 3,900				$ 3,900		4,000	$ 3,900
Internal Revenue Service (IRS) \| Federal
Operating Loss Carryforwards [Line Items]
Net operating losses	$ 200										$ 200

Income Taxes - Deferred Income Tax (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred income tax assets
Allowance for doubtful accounts	$ 838	$ 969
Inventory	265	236
Intangible assets	2,255	2,529
Accrued expenses	2,560	5,157
Net operating loss carryforward	3,729	4,094
Capital lease obligations	1,004	1,140
Capital losses	463	719
Foreign tax credit carryover	618	0
Deferred share-based compensation	4,080	5,802
Other	484	285
Deferred income tax assets	16,296	20,931
Valuation allowance	(4,044)	(3,896)
Net deferred income tax assets	12,252	17,035
Deferred income tax liabilities
Property and equipment	(6,893)	(8,655)
Goodwill	(6,578)	(13,586)
Intangible assets	(5,972)	(5,051)
Other	(6)	(11)
Deferred income tax liabilities	(19,449)	(27,303)
Net deferred income taxes	$ (7,197)	$ (10,268)

Income Taxes - Changes in Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	7 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2017
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at beginning of period	$ 303	$ 267
Additions for tax positions related to the current fiscal period	8	11
Additions for tax positions related to prior years	0	188
Decreases for tax positions related to prior years	(11)	0
Impact of foreign exchange fluctuation	0	10
Settlements	0	(198)
Reductions related to the expiration of statutes of limitations	(33)	(122)
Balance at end of period	$ 267	$ 156

Employee Benefit Plans (Details) - USD ($) $ in Millions	7 Months Ended	12 Months Ended
Employee Benefit Plans (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2017	May 31, 2016	May 31, 2015
401(k) savings plan
Minimum age for employees to contribute catch up contributions under IRS limits		50 years
Continuous service period required for eligibility of employees to participate under the plan		3 months
Maximum Company match amount of employee contributions matched up to 6% of annual compensation (as a percent)		50.00%
Maximum percentage of employee's annual compensation for which the company contributes a matching contribution (as a percent)		6.00%
Vesting period for employer matching contribution		5 years
Contribution under 401(k) savings plan	$ 2.0	$ 3.7	$ 3.5	$ 3.0
Multiemployer Plans, Pension \| Boilermakers and Pipefitters Plans
Multiemployer Defined Benefit Pension Plans
Multiemployer plan funded status		Between 65 and less than 80 percent
Multiemployer plan, amount of Company's contributions	$ 1.5	$ 2.4	$ 2.5	$ 2.5
Multiemployer plan, Company's contributions as percentage of total		5.00%

Related Party Transactions (Details) $ in Millions	12 Months Ended
Related Party Transactions (Details) $ in Millions	Dec. 31, 2017 USD ($) director	Aug. 17, 2016 shares
Shareholder and officer
Related Party Transactions
Total rent payments	$ 0.9
Non-employee director \| Capital Management Enterprise (“CME”) \| Consulting Services
Related Party Transactions
Number of non-employee director \| director	1
France \| Shareholder and officer
Related Party Transactions
Total rent payments	$ 0.2
Brazil \| Shareholder and officer
Related Party Transactions
Total rent payments	$ 0.1
Stock Repurchase Plan \| Chairman and CEO
Related Party Transactions
Number of shares authorized to be repurchased (in shares) \| shares		1,000,000

Obligations under Capital Leases (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Obligations under capital leases
Net book value of assets under capital lease	$ 19,500	$ 17,600
Future minimum lease payments
2018	5,899
2019	3,788
2020	2,485
2021	1,778
2022	634
Thereafter	760
Total minimum lease payments	15,344
Less: amount representing interest	(731)
Present value of minimum lease payments	14,613
Less: current portion of obligations under capital leases	(5,875)	(6,488)
Obligations under capital leases, net of current portion	8,738	$ 9,682
Minimum
Obligations under capital leases
Required monthly payments	$ 1
Effective interest rate (as a percent)	1.00%
Maximum
Obligations under capital leases
Required monthly payments	$ 73
Effective interest rate (as a percent)	7.00%

Commitments and Contingencies - Minimum Lease Payments (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Commitments and Contingencies Disclosure [Abstract]
2018	$ 11,542
2019	8,888
2020	6,902
2021	4,881
2022	4,304
Thereafter	12,915
Total	$ 49,432

Commitments and Contingencies - Narrative (Details) - USD ($)	1 Months Ended			3 Months Ended	7 Months Ended		12 Months Ended
	Feb. 28, 2018	Nov. 30, 2016	Sep. 30, 2016	May 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	May 31, 2016	May 31, 2015
Litigation
Total rent expense					$ 6,600,000		$ 11,800,000		$ 11,200,000	$ 10,600,000
Legal settlement charges					$ 0	$ 0	$ 1,600,000	$ 6,320,000	$ 6,320,000	$ 0
Period over which potential acquisition-related contingent consideration would be payable							2 years 6 months
Triumph Aerostructures-Vought Aircraft Division v Mistras Group \| Subsequent Event
Litigation
Litigation settlement amount	$ 1,600,000
Consolidated class and collective action lawsuit \| Edgar Viceral and David Kruger v Mistras Group
Litigation
Payroll taxes and other cost related to settlement				$ 6,300,000
Lawsuits for alleged quality defects \| AGL Services Company v Mistras Group
Litigation
Verbal demand for damages		$ 5,800,000
Dispute with former owner of company's French subsidiary \| French Subsidiary \| AGL Services Company v Mistras Group
Litigation
Litigation settlement amount				$ 400,000
Damages from product defects \| Triumph Aerostructures-Vought Aircraft Division v Mistras Group \| Ultrasonic Inspection System
Litigation
Verbal demand for damages			$ 2,300,000
Legal settlement charges							$ 1,600,000
Acquisition-related contingencies
Litigation
Potential acquisition-related contingent consideration, low end of range							0
Potential acquisition-related contingent consideration, high end of range							$ 8,500,000

Segment Disclosure - Financial Information (Details) $ in Thousands	3 Months Ended								7 Months Ended		12 Months Ended
	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2017 USD ($) Operating_Segment	Dec. 31, 2016 USD ($)	May 31, 2016 USD ($)	May 31, 2015 USD ($)
Segment Reporting [Abstract]
Number of operating segments \| Operating_Segment											3
Financial information by segment
Revenues	$ 187,643	$ 179,570	$ 170,439	$ 163,318	$ 170,156	$ 168,811	$ 178,340	$ 167,455	$ 404,161	$ 427,913	$ 700,970	$ 684,762	$ 719,181	$ 711,252
Gross profit	50,319	47,897	46,343	43,153	47,978	50,651	51,535	43,970	117,004	123,190	187,712	194,134	203,008	184,733
Income from operations	6,282	$ (10,375)	$ 5,003	$ 3,250	2,944	$ 12,116	$ 4,840	$ 5,646	17,533	$ 35,098	4,160	25,546	43,177	30,353
Depreciation and amortization									19,199		31,383		32,474	33,286
Intangible assets, net	63,739				40,007				40,007		63,739	40,007
Total assets	554,441				469,427				469,427		554,441	469,427
Operating segments \| Services
Financial information by segment
Revenues									293,218		543,565		553,279	540,224
Gross profit									75,784		139,160		145,262	135,201
Income from operations									22,411		46,677		52,552	49,142
Depreciation and amortization									12,765		21,649		22,725	22,268
Intangible assets, net	46,864				19,550				19,550		46,864	19,550
Total assets	377,585				291,539				291,539		377,585	291,539
Operating segments \| International
Financial information by segment
Revenues									104,013		144,265		143,025	146,953
Gross profit									34,210		38,974		43,613	34,572
Income from operations									10,597		3,537		9,293	(575)
Depreciation and amortization									5,306		7,768		7,774	8,451
Intangible assets, net	13,899				14,139				14,139		13,899	14,139
Total assets	150,779				130,427				130,427		150,779	130,427
Operating segments \| Products and Systems
Financial information by segment
Revenues									14,541		23,297		30,293	31,255
Gross profit									6,920		9,798		14,022	14,314
Income from operations									(254)		(16,991)		2,688	2,461
Depreciation and amortization									1,372		2,180		2,323	2,426
Intangible assets, net	2,261				5,482				5,482		2,261	5,482
Total assets	12,733				28,964				28,964		12,733	28,964
Corporate and eliminations
Financial information by segment
Revenues									(7,611)		(10,157)		(7,416)	(7,180)
Gross profit									90		(220)		111	646
Income from operations									(15,221)		(29,063)		(21,356)	(20,675)
Depreciation and amortization									(244)		(214)		$ (348)	$ 141
Intangible assets, net	715				836				836		715	836
Total assets	$ 13,344				$ 18,497				$ 18,497		$ 13,344	$ 18,497

Segment Disclosure - Revenue and Long-lived Assets (Details) - USD ($) $ in Thousands	3 Months Ended								7 Months Ended		12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	May 31, 2016	May 31, 2015
Revenue and long-lived assets by geographic area
Revenue	$ 187,643	$ 179,570	$ 170,439	$ 163,318	$ 170,156	$ 168,811	$ 178,340	$ 167,455	$ 404,161	$ 427,913	$ 700,970	$ 684,762	$ 719,181	$ 711,252
Long-lived assets	354,320				283,097				283,097		354,320	283,097
United States
Revenue and long-lived assets by geographic area
Revenue									256,926		466,683		519,361	491,818
Long-lived assets	237,616				186,960				186,960		237,616	186,960
Other Americas
Revenue and long-lived assets by geographic area
Revenue									41,777		86,870		67,809	68,628
Long-lived assets	36,011				29,065				29,065		36,011	29,065
Europe
Revenue and long-lived assets by geographic area
Revenue									91,847		132,421		118,566	137,071
Long-lived assets	$ 80,693				$ 67,072				67,072		80,693	$ 67,072
Asia-Pacific
Revenue and long-lived assets by geographic area
Revenue									$ 13,611		$ 14,996		$ 13,445	$ 13,735

Repurchase of Common Stock (Details) - USD ($)		7 Months Ended	12 Months Ended	27 Months Ended
Repurchase of Common Stock (Details) - USD ($)	Aug. 17, 2016	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2017	Oct. 07, 2015
Class of Stock [Line Items]
Treasury stock acquired, aggregate cost		$ 9,000,000	$ 15,923,000
Stock Repurchase Plan
Class of Stock [Line Items]
Stock repurchase plan, amount approved					$ 50,000,000
Treasury stock repurchased (in shares)		146,000
Treasury stock acquired, average price (in dollars per share)		$ 20.48
Treasury stock acquired, aggregate cost		$ 3,000,000
Stock repurchase plan, remaining amount approved			$ 25,100,000	$ 25,100,000
Stock Repurchase Plan \| Chairman and CEO
Class of Stock [Line Items]
Stock repurchase plan, amount approved (in shares)	1,000,000
Stock repurchase plan, amount approved each month from CEO	$ 2,000,000
Average daily price of common stock for the preceding month discount, percent	2.00%
Treasury stock repurchased (in shares)		274,000	726,000	1,000,000
Treasury stock acquired, average price (in dollars per share)		$ 21.90	$ 21.93	$ 21.92
Treasury stock acquired, aggregate cost		$ 6,000,000	$ 15,900,000	$ 21,900,000

Twelve Months Ended December 31, 2016 and Seven Months Ended December 31, 2015 Comparative Data (Unaudited) - Condensed Consolidated Statement of Income (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								7 Months Ended		12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	May 31, 2016	May 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Revenue	$ 187,643	$ 179,570	$ 170,439	$ 163,318	$ 170,156	$ 168,811	$ 178,340	$ 167,455	$ 404,161	$ 427,913	$ 700,970	$ 684,762	$ 719,181	$ 711,252
Cost of revenue									274,298	292,718	492,238	468,929	494,911	506,281
Depreciation									12,859	12,005	21,020	21,699	21,262	20,238
Gross profit	50,319	47,897	46,343	43,153	47,978	50,651	51,535	43,970	117,004	123,190	187,712	194,134	203,008	184,733
Selling, general and administrative expenses									91,058	81,117	153,025	148,914	141,229	143,978
Research and engineering									1,577	1,431	2,272	2,670	2,523	2,521
Depreciation and amortization									6,340	6,503	10,363	10,689	11,212	13,048
Litigation charges									0	0	1,600	6,320	6,320	0
Acquisition-related benefit, net									496	(959)	482	(5)	(1,453)	(5,167)
Income from operations	6,282	(10,375)	5,003	3,250	2,944	12,116	4,840	5,646	17,533	35,098	4,160	25,546	43,177	30,353
Interest expense, net										3,672		3,075
(Loss) income before provision for income taxes									15,481	31,426	(226)	22,471	38,415	25,731
Provision for income taxes									5,870	11,627	1,942	8,008	13,765	9,740
Net (loss) income									9,611	19,799	(2,168)	14,463	24,650	15,991
Less: Net income (loss) attributable to non-controlling interests									43	(15)	7	54	(4)	(90)
Net (loss) income attributable to Mistras Group, Inc.	$ 884	$ (6,968)	$ 2,217	$ 1,692	$ 963	$ 7,238	$ 2,761	$ 3,447	$ 9,568	$ 19,814	$ (2,175)	$ 14,409	$ 24,654	$ 16,081
Basic (in dollars per share)	$ 0.03	$ (0.25)	$ 0.08	$ 0.06	$ 0.03	$ 0.25	$ 0.10	$ 0.12	$ 0.33	$ 0.69	$ (0.08)	$ 0.50	$ 0.85	$ 0.56
Diluted (in dollars per share)	$ 0.03	$ (0.25)	$ 0.07	$ 0.06	$ 0.03	$ 0.24	$ 0.09	$ 0.11	$ 0.32	$ 0.67	$ (0.08)	$ 0.48	$ 0.82	$ 0.54
Basic (in shares)									28,989	28,810	28,422	28,960	28,856	28,613
Diluted (in shares)									30,125	29,676	28,422	30,114	29,891	29,590

Selected Quarterly Financial Information (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								7 Months Ended		12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	May 31, 2016	May 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 187,643	$ 179,570	$ 170,439	$ 163,318	$ 170,156	$ 168,811	$ 178,340	$ 167,455	$ 404,161	$ 427,913	$ 700,970	$ 684,762	$ 719,181	$ 711,252
Gross Profit	50,319	47,897	46,343	43,153	47,978	50,651	51,535	43,970	117,004	123,190	187,712	194,134	203,008	184,733
Income from operations	6,282	(10,375)	5,003	3,250	2,944	12,116	4,840	5,646	17,533	35,098	4,160	25,546	43,177	30,353
Net (loss) income attributable to Mistras Group, Inc.	$ 884	$ (6,968)	$ 2,217	$ 1,692	$ 963	$ 7,238	$ 2,761	$ 3,447	$ 9,568	$ 19,814	$ (2,175)	$ 14,409	$ 24,654	$ 16,081
Earnings per common share:
Basic (in dollars per share)	$ 0.03	$ (0.25)	$ 0.08	$ 0.06	$ 0.03	$ 0.25	$ 0.10	$ 0.12	$ 0.33	$ 0.69	$ (0.08)	$ 0.50	$ 0.85	$ 0.56
Diluted (in dollars per share)	$ 0.03	$ (0.25)	$ 0.07	$ 0.06	$ 0.03	$ 0.24	$ 0.09	$ 0.11	$ 0.32	$ 0.67	$ (0.08)	$ 0.48	$ 0.82	$ 0.54

- Definition

The amount of net income (loss) from continuing operations per each share of common stock or unit outstanding during the reporting period.

+ References + Details

- Definition

The amount of net income (loss) derived from continuing operations during the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

+ References + Details