Payments of severance obligations Loss Contingency Accrual, Payments Supplemental disclosure of cash paid Supplemental Cash Flow Information [Abstract] Customer [Domain] Customer [Domain] Foreign currency loss Foreign Currency Transaction Gain (Loss), Realized Percentage of settlement installments Litigation Settlement, Amount Awarded from Other Party, Installment Percentage Litigation Settlement, Amount Awarded from Other Party, Installment Percentage Earnings (loss) per Share Earnings Per Share, Policy [Policy Text Block] Office furniture and equipment Office Furniture and Equipment [Member] Furniture and equipment commonly used in offices and stores that have no permanent connection to the structure of a building or utilities. 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Accumulated Amortization Finite-Lived Intangible Assets, Accumulated Amortization Goodwill Goodwill Disclosure [Text Block] Statistical Measurement [Domain] Statistical Measurement [Domain] Due diligence, professional fees and other transaction costs Business Combination, Acquisition Related Costs Entity Address, Address Line One Entity Address, Address Line One Other Other Intangible Assets [Member] Segment Disclosure Segment Reporting, Policy [Policy Text Block] Consideration received on sale of subsidiary Disposal Group, Including Discontinued Operation, Consideration Proceeds from sale of equipment Proceeds from Sale of Property, Plant, and Equipment Forfeited (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value Revenue from Contract with Customer [Abstract] Revenue from Contract with Customer [Abstract] Entity Filer Category Entity Filer Category Operating leases Operating Lease, Weighted Average Remaining Lease Term Other assets Other Assets, Noncurrent Deferral period of rental payments Operating Lease, Deferral Period Of Rental Payments Operating Lease, Deferral Period Of Rental Payments Dilutive effect of stock options outstanding (in shares) Incremental Common Shares Attributable to Stock Options Outstanding Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of stock options outstanding. Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Segments [Axis] Segments [Axis] Dividend yield Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate Number of awards that may be granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant Net change in cash and cash equivalents Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] Share-based payments APIC, Share-based Payment Arrangement, Increase for Cost Recognition Other Other Long Term Debt [Member] Represents details pertaining to other long-term debt of the entity. Income taxes payable Increase (Decrease) in Income Taxes Payable Adjustments to preliminary purchase price allocations Goodwill, Purchase Accounting Adjustments Expired or forfeited (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period Tax Credit Carryforward [Line Items] Tax Credit Carryforward [Line Items] Document Fiscal Year Focus Document Fiscal Year Focus Lessee, Lease, Description [Line Items] Lessee, Lease, Description [Line Items] Amortization expense of intangibles Amortization of Intangible Assets Dilutive effect of restricted stock units outstanding (in shares) Incremental Common Shares Attributable to Restricted Stock Units Outstanding Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of restricted stock units outstanding. Variable lease expense Variable Lease, Cost Operating leases Operating Lease, Weighted Average Discount Rate, Percent Potentially dilutive shares excluded from computation of diluted EPS due to net income (loss) for the period (in shares) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Revenue recognized that was included in contract liability balance at the beginning of the year Contract with Customer, Liability, Revenue Recognized Impairment Finite-Lived Intangible Assets, Accumulated Impairment Finite-Lived Intangible Assets, Accumulated Impairment Liability Class [Axis] Liability Class [Axis] Company's Headquarters Building [Member] Schedule of Vesting Activity of Restricted Stock Unit Awards Share-based Compensation Arrangements by Share-based Payment Award, Restricted Stock Units, Vested and Expected to Vest [Table Text Block] Schedule of Supplemental Balance Sheet Information Assets And Liabilities, Lessee [Table Text Block] Assets And Liabilities, Lessee Business Combination and Asset Acquisition [Abstract] Business Acquisition [Axis] Business Acquisition [Axis] Granted (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value Fair value of awards vested Grant date fair value of awards issued Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value Legal settlement and litigation charges, net Contingency charges Loss Contingency, Loss in Period Services Services [Member] Represents Services, a business segment of the entity. 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Liability [Abstract] Right-Of-Use Asset Obtained In Exchange For Lease Liability ASSETS Assets Assets [Abstract] Cumulative goodwill impairment Goodwill, Impaired, Accumulated Impairment Loss Land Land [Member] Senior Secured Term Loan Senior Secured Term Loan A Facility Term A Loan Facility [Member] Term A Loan Facility Finance leases Right-of-Use Asset Obtained in Exchange for Finance Lease Liability Other Other Products and Services [Member] Other Products and Services Granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Preferred stock, 10,000,000 shares authorized Preferred Stock, Value, Issued Performance condition adjustments (in shares) Share-Based Compensation Arrangement By Share-Based Payment Award, Equity Instruments Other Than Options, Increase (Decrease) Adjustments In Period Share-Based Compensation Arrangement By Share-Based Payment Award, Equity Instruments Other Than Options, Increase (Decrease) Adjustments In Period Stok option award outstanding (in shares) Outstanding at beginning of period (in shares) Outstanding at end of period (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number Entity Address, City or Town Entity Address, City or Town Retained earnings (deficit) Retained Earnings [Member] Debt Instrument [Axis] Debt Instrument [Axis] Prepaid expenses and other assets Increase (Decrease) in Prepaid Expense and Other Assets Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Number of settlement installments Litigation Settlement, Amount Awarded from Other Party, Number Of Installments Litigation Settlement, Amount Awarded from Other Party, Number Of Installments Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Certain Acquired Companies Series of Individually Immaterial Business Acquisitions [Member] Thereafter Finance Lease, Liability, To Be Paid, After Year Four Finance Lease, Liability, To Be Paid, After Year Four Related Party [Axis] Related Party [Axis] Accounts receivable Increase (Decrease) in Accounts Receivable Operating leases Right-of-Use Asset Obtained in Exchange for Operating Lease Liability Germany GERMANY Property, Plant and Equipment, net Property, Plant and Equipment [Line Items] Award vesting percentage (ratably on each of the first four anniversary date) Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Disclosure [Abstract] Weighted-average remaining lease term (in years) Weighted Average Remaining Lease Term [Abstract] Weighted Average Remaining Lease Term Comprehensive Income (Loss) Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to 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shares outstanding (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Document Type Document Type Capitalized costs associated with debt modifications Unamortized Debt Issuance Expense Schedule of Disaggregated Revenues Disaggregation of Revenue [Table Text Block] Reporting Unit [Domain] Reporting Unit [Domain] Thereafter Lessee, Operating Lease, Liability, To Be Paid, After Year Four Lessee, Operating Lease, Liability, To Be Paid, After Year Four Restricted Stock Units Awards (Units) Performance Restricted Stock (Units) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Diluted income (loss) per share: Earnings Per Share, Diluted [Abstract] Class Action Class Action [Member] Class Action Entity Current Reporting Status Entity Current Reporting Status Machinery and equipment Machinery and Equipment [Member] Weighted Average Grant-Date Fair Value (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract] Products Products and Systems Products and Systems [Member] Products and Systems Net settlement of restricted stock units Share-based Payment Arrangement, Decrease for Tax Withholding Obligation Total rent payments Operating - operating cash flows Operating Lease, Payments Total number of shares authorized for issuance (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized Other Other Noncash Income (Expense) Potential acquisition-related contingent consideration, low end of range Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, Low Accounts receivable, net Accounts receivable, net Past due receivables outstanding Receivables, Net, Current Revenue, Remaining Performance Obligation, Expected 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Goodwill, Impairment Loss Less: Foreign currency translation adjustments attributable to noncontrolling interests Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax, Portion Attributable to Noncontrolling Interest Fair Value by Liability Class [Domain] Fair Value by Liability Class [Domain] Document Transition Report Document Transition Report Power Generation & Transmission Power Generation and Transmission [Member] Power Generation and Transmission Operating Lessee, Operating Lease, Liability, Payment, Due [Abstract] Finite-Lived Intangible Assets [Line Items] Finite-Lived Intangible Assets [Line Items] Total liabilities and equity Liabilities and Equity Other accrued expenses Other Accrued Liabilities, Current Deferred revenue Contract with Customer, Liability, Current Anniversary 1 Share-based Payment Arrangement, Tranche One [Member] Infrastructure, Research & Engineering Infrastructure, Research and Engineering [Member] Infrastructure, Research and Engineering Covenants not to compete Noncompete Agreements [Member] Exercised (in dollars per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price Right to Customer Contracts Right to Customer Contracts [Member] Right to Customer Contracts Additional paid-in capital Additional Paid in Capital Lessee, Lease, Description [Table] Lessee, Lease, Description [Table] Brazilian Reporting Unit Brazilian Reporting Unit [Member] Brazilian Reporting Unit LIABILITIES AND EQUITY Liabilities and Equity [Abstract] Acquisitions Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Purchases Cash flows from operating activities Net Cash Provided by (Used in) Operating Activities, Continuing Operations [Abstract] Impairment of ROU assets Operating Lease, Impairment Loss Earnings (loss) per Share Earnings Per Share [Text Block] Minimum Minimum [Member] Adjustments to fair value of contingent consideration liabilities Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability Foreign Subsidiary Affiliated Entity [Member] Gross profit Gross profit Gross Profit 2023 Lessee, Operating Lease, Liability, to be Paid, Year Two Outstanding borrowings Long-term Line of Credit Effect of exchange rate changes on cash and cash equivalents Effect of Exchange Rate on Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Selling, general and administrative expenses Selling, General and Administrative Expense Unamortized debt issuance costs Debt Issuance Costs, Net Expired or forfeited (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period, Weighted Average Exercise Price Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table] Reclassification Reclassification, Comparability Adjustment [Policy Text Block] Preferred stock, shares authorized (in shares) Preferred Stock, Shares Authorized Income Tax Authority [Domain] Income Tax Authority [Domain] Leases Lessee, Finance Leases [Text Block] Fair value adjustments to contingent consideration Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Financial Liabilities Trading Symbol Trading Symbol Amount of damages claimed Loss Contingency, Damages Sought, Value Deferred income taxes Deferred Income Tax Assets, Net Current Liabilities Liabilities, Current [Abstract] December 31, 2021 Debt Covenant Period Two [Member] Debt Covenant Period Two Acquisition of business, net of cash acquired Payments to Acquire Businesses, Net of Cash Acquired Share-Based Compensation Share-based Payment Arrangement [Text Block] Level 3 Fair Value, Inputs, Level 3 [Member] Accumulated depreciation and amortization Property, Plant, and Equipment and Finance Lease Right-of-Use Asset, Accumulated Depreciation and Amortization Accounting Policies [Abstract] September 30, 2021 Debt Covenant Period One [Member] Debt Covenant Period One 2016 Plan Long-Term Incentive Plan 2016 [Member] Long-Term Incentive Plan 2016 Total ROU liabilities ROU liabilities Lease liability Operating Lease, Liability Outstanding letters of credit Letters of Credit Outstanding, Amount Common stock, $0.01 par value, 200,000,000 shares authorized, 29,457,605 and 29,234,143 shares issued and outstanding Common Stock, Value, Issued Finance leases Finance Lease, Weighted Average Discount Rate, Percent Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] Amount of purchased commitment to buy products from the buyer on sale of subsidiary Long-term Purchase Commitment, Amount Contingent Consideration Contingent Consideration [Member] Contingent Consideration Weighted-average period over which unrecognized compensation cost is expected to be recognized (years) Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition Outstanding at the beginning of period (in dollars per share) Outstanding at end of period (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value Goodwill acquired during the period Goodwill, Acquired During Period Basis of Presentation Basis of Accounting, Policy [Policy Text Block] PRSUs Performance Shares [Member] Commitments and contingencies Commitments and Contingencies Leases Lessee, Operating Leases [Text Block] Accumulated other comprehensive loss Accumulated Other Comprehensive Income (Loss), Net of Tax Amortization of ROU assets Finance Lease, Right-of-Use Asset, Amortization Allowance for credit losses Accounts Receivable, Allowance for Credit Loss, Current Remainder of 2021 Lessee, Operating Lease, Liability, to be Paid, Remainder of Fiscal Year Acquisitions Business Combination Disclosure [Text Block] Restricted Stock Restricted Stock [Member] Payment of financing costs Finance costs incurred Payments of Debt Issuance Costs Receivables [Abstract] Receivables [Abstract] Disposal Group Classification [Axis] Disposal Group Classification [Axis] Antidilutive Securities, Name [Domain] Antidilutive Securities, Name [Domain] Document Period End Date Document Period End Date Total consolidated debt leverage ratio Debt Instrument, Covenant Compliance, Total Consolidated Debt Leverage Ratio Debt Instrument, Covenant Compliance, Total Consolidated Debt Leverage Ratio Goodwill [Line Items] Goodwill [Line Items] Entity Registrant Name Entity Registrant Name Less: Present value discount Lessee, Operating Lease, Liability, Undiscounted Excess Amount Income Tax Authority [Axis] Income Tax Authority [Axis] Contingent consideration payment period based upon achievement of specific performance metrics Business Combination, Contingent Consideration Payment Period Business Combination, Contingent Consideration Payment Period Prepaid expenses and other current assets Prepaid Expense and Other Assets, Current Revenue Revenue Revenue from Contract with Customer, Excluding Assessed Tax Other Americas Other Americas [Member] Represents the information pertaining to North and South America excluding the United States. Less: Present value discount Finance Lease, Liability, Undiscounted Excess Amount Accounts Receivable, net Loans, Notes, Trade and Other Receivables Disclosure [Text Block] Stock Options Share-based Payment Arrangement, Option [Member] Acquisition and Disposition Related Contingencies Acquisition Related Contingencies [Member] Represents the contingencies pertaining to business acquisitions by the entity. Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Consolidation Items [Domain] Consolidation Items [Domain] Class Action on Behalf of Employees Class Action on Behalf Of Current And Former Employees [Member] Class Action on Behalf Of Current And Former Employees Common Stock Common Stock [Member] Variable Rate [Axis] Variable Rate [Axis] Segment Disclosure Segment Reporting Disclosure [Text Block] Finance leases Finance Lease, Weighted Average Remaining Lease Term Income (loss) from operations Income (loss) from operations Operating Income (Loss) Number of performance award metrics Share-Based Compensation Arrangement By Share-Based Payment Award, Number Of Award Metrics Share-Based Compensation Arrangement By Share-Based Payment Award, Number Of Award Metrics Property, Plant and Equipment [Table] Property, Plant and Equipment [Table] Right-of-use liability - Operating ROU - current Operating Lease, Liability, Current Description of Business and Basis of Presentation Organization, Consolidation and Presentation of Financial Statements Disclosure and Significant Accounting Policies [Text Block] Increase (Decrease) in Stockholders' Equity Increase (Decrease) in Stockholders' Equity [Roll Forward] Property, Plant and Equipment [Abstract] Property, Plant and Equipment [Abstract] Share-based compensation expense Share-based Payment Arrangement, Noncash Expense Variable Rate [Domain] Variable Rate [Domain] Additional paid-in capital Additional Paid-in Capital [Member] Cash and cash equivalents Cash balance Cash and Cash Equivalents, at Carrying Value Depreciation expense Depreciation Settlement amount Litigation Settlement, Amount Awarded from Other Party Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Proceeds from revolver Proceeds from Lines of Credit Impairment charges Asset Impairment Charges Operating Lease, Liability, Current, Statement of Financial Position [Extensible List] Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration] Anniversary 4 Share-based Compensation Award, Tranche Four [Member] Share-based Compensation Award, Tranche Four Purchase of property, plant and equipment Payments to Acquire Property, Plant, and Equipment Maximum Maximum [Member] Share-based Payment Arrangement [Abstract] Share-based Payment Arrangement [Abstract] Loss Contingency, Nature [Domain] Loss Contingency, Nature [Domain] Total liabilities Liabilities Intangible Assets, Net (Excluding Goodwill) [Abstract] Intangible Assets, Net (Excluding Goodwill) [Abstract] Each quarter through March 31, 2022 Debt Covenant Period Three [Member] Debt Covenant Period Three Award Type [Axis] Award Type [Axis] Granted (in dollars per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price Schedule of Maturities of Operating Lease Liabilities Lessee, Operating Lease, Liability, Maturity [Table Text Block] Consolidation Items [Axis] Consolidation Items [Axis] Total Mistras Group, Inc. stockholders’ equity Stockholders' Equity Attributable to Parent Common stock, shares issued (in shares) Common Stock, Shares, Issued Payments Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements Term of agreement to purchase products from the buyer on sale of subsidiary Long-term Purchase Commitment, Period Goodwill and Intangible Assets Disclosure [Abstract] Goodwill and Intangible Assets Disclosure [Abstract] Intangible Assets Intangible Assets Disclosure [Text Block] Useful Life (Years) Property, Plant and Equipment, Useful Life 2009 Plan Long Term Incentive Plan 2009 [Member] Represents information pertaining to 2009 Long-Term Incentive Plan, which becomes effective upon the closing of the IPO. ROU liability - long-term Operating Lease, Liability, Noncurrent Total Finance Lease, Liability, Payment, Due Schedule of Fully-vested Common Stock Issued to Non-employee Directors Schedule of Deferred Compensation Arrangement with Individual, Share-based Payments [Table Text Block] Interest expense Interest Expense 2022 Finance Lease, Liability, to be Paid, Year One Number of equity incentive plans Number Of Employee Share-Based Plans Number Of Employee Share-Based Plans Loss Contingency Nature [Axis] Loss Contingency Nature [Axis] City Area Code City Area Code COVID-19 COVID-19 Pandemic [Member] COVID-19 Pandemic Accumulated Deficit Retained Earnings (Accumulated Deficit) Texas Customer Texas Customer [Member] Texas Customer Operating segments Operating Segments [Member] Litigation Case [Domain] Litigation Case [Domain] Each quarter thereafter Debt Covenant Period Four [Member] Debt Covenant Period Four Restricted Stock Unit Awards Restricted Stock Units (RSUs) [Member] Statement of Stockholders' Equity [Abstract] Statement of Stockholders' Equity [Abstract] Accrued workers’ compensation and health benefits Accrued Workers Compensation and Health Benefits Current Carrying value as of the balance sheet date of obligations and payables pertaining to workers compensation and health benefits. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle, if longer). Lease liability Finance Lease, Liability Anniversary 2 Share-based Payment Arrangement, Tranche Two [Member] Income Statement [Abstract] Income Statement [Abstract] Amendment Flag Amendment Flag Foreign currency translation Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Foreign Currency Translation Adjustments Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Foreign Currency Translation Adjustments Schedule of Company's Outstanding, Nonvested Restricted Share Units and Performance Restricted Stock Units Share-based Payment Arrangement, Outstanding Award, Activity, Excluding Option [Table Text Block] Foreign Subsidiaries Disposal Of Foreign Subsidiaries [Member] Disposal Of Foreign Subsidiaries [Member] Repayment of revolver Repayments of Lines of Credit 2024 Finance Lease, Liability, to be Paid, Year Three 2025 Finance Lease, Liability, to be Paid, Year Four Other Process Industries Other Process Industries [Member] Other Process Industries 2023 Finance Lease, Liability, to be Paid, Year Two Related Party Transaction [Axis] Related Party Transaction [Axis] Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets by Major Class [Axis] Provision (benefit) for income taxes Income Tax Expense (Benefit) Total equity Beginning balance Ending balance Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Accrued expenses and other liabilities Increase (Decrease) in Other Accrued Liabilities and Deferred Liabilities The increase (decrease) during the reporting period in other expenses incurred but not yet paid and the change during the period in carrying value for all deferred liabilities due within one year or operating cycle. Asia-Pacific Asia Pacific [Member] Proceeds from borrowings of long-term debt Proceeds from Issuance of Long-term Debt Equity Components [Axis] Equity Components [Axis] Fair Value Disclosures [Abstract] Fair Value Disclosures [Abstract] Antidilutive Securities [Axis] Antidilutive Securities [Axis] Purchase of intangible assets Payments to Acquire Intangible Assets and Software The cash outflow to acquire assets without physical form usually arising from contractual or other legal rights, excluding goodwill. In addition, the cash outflow associated with the development, modification or acquisition of software programs or applications for internal use (that is, not to be sold, leased or otherwise marketed to others) that qualify for capitalization. Total current assets Assets, Current Total Lessee, Operating Lease, Liability, to be Paid Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] Senior debt to EBITDA ratio Debt Instrument, Covenant Compliance, Senior Debt To Earnings Before Income Taxes, Depreciation And Amortization Ratio Debt Instrument, Covenant Compliance, Senior Debt To Earnings Before Income Taxes, Depreciation And Amortization Ratio Forfeited (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period Inventories Inventory, Net Schedule of Selected Consolidated Financial Information by Segment Schedule of Segment Reporting Information, by Segment [Table Text Block] Valuation allowance recorded during the period related to deferred tax assets Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Amount Accrued Expenses and Other Current Liabilities Accrued Liabilities Deferred Revenues and Contingent Consideration Liabilities Current Disclosure [Text Block] The entire disclosure for accrued liabilities, deferred revenues, and the fair value of contingent consideration liabilities at the end of the reporting period. Entity File Number Entity File Number Fair value measurements Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Statement of Financial Position [Abstract] Statement of Financial Position [Abstract] Fair Value Measurements Fair Value Measurement, Policy [Policy Text Block] Unrecognized compensation costs Share-based Payment Arrangement, Nonvested Award, Option, Cost Not yet Recognized, Amount Current portion of long-term debt Less: Current portion Long-term Debt, Current Maturities Product and Service [Axis] Product and Service [Axis] Property, Plant and Equipment, Type [Domain] Long-Lived Tangible Asset [Domain] Cash flows from financing activities Net Cash Provided by (Used in) Financing Activities, Continuing Operations [Abstract] Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Entity Small Business Entity Small Business Unrecognized compensation cost, net of estimated forfeitures Unrecognized compensation cost Share-based Payment Arrangement, Nonvested Award, Excluding Option, Cost Not yet Recognized, Amount Equity Component [Domain] Equity Component [Domain] Short-term lease expense Short-term Lease, Cost 2022 Lessee, Operating Lease, Liability, to be Paid, Year One Foreign currency translation adjustments Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax Disposal Group Name [Domain] Disposal Group Name [Domain] Schedule of Accounts, Notes, Loans and Financing Receivable [Table] Schedule of Accounts, Notes, Loans and Financing Receivable [Table] Awards issued (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period Pension accrual Multiemployer Plans, Withdrawal Obligation Corp/Elim Corporate and eliminations Corporate And Eliminations [Member] Corporate And Eliminations Statement Statement [Line Items] Litigation Case [Axis] Litigation Case [Axis] International International [Member] Represents International, a business segment of the entity. Property, plant and equipment, net Property, plant and equipment, net Property, Plant, and Equipment and Finance Lease Right-of-Use Asset, after Accumulated Depreciation and Amortization Various Pipeline Projects for Texas Customer Various Pipeline Projects For Texas Customer [Member] Various Pipeline Projects For Texas Customer Impairment of intangibles Impairment of Intangible Assets, Finite-lived Settlement liability Litigation Settlement, Amount Awarded to Other Party Executive and Senior Officers Executive and Senior Officers [Member] Represents information pertaining to the executives and senior officers of the reporting entity. Weighted Average Exercise Price Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract] Operating Lease Arrangement Operating Lease Arrangement [Member] Operating Lease Arrangement Liabilities Liabilities [Abstract] Potential acquisition-related contingent consideration, high end of range Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High 2025 Lessee, Operating Lease, Liability, to be Paid, Year Four Debt Disclosure [Abstract] Debt Disclosure [Abstract] Entity Address, State or Province Entity Address, State or Province Current portion of finance lease obligations Finance Lease, Liability, Current Income (loss) before benefit for income taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Property, Plant and Equipment, Type [Axis] Long-Lived Tangible Asset [Axis] Segment Reporting [Abstract] Segment Reporting [Abstract] Useful Life (Years) Finite-Lived Intangible Asset, Useful Life Customer [Axis] Customer [Axis] Interest on lease liabilities Finance Lease, Interest Expense Number of welds inspected (over) Loss Contingency, Number Of Welds Inspected Loss Contingency, Number Of Welds Inspected Accounts payable Increase (Decrease) in Accounts Payable, Trade Revaluation Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Increase (Decrease) Due To Changes In Amount Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Increase (Decrease) Due To Changes In Amount Schedule of Computations of Basic and Diluted Earnings (Loss) per Share Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross Entity Shell Company Entity Shell Company Local Phone Number Local Phone Number Finance Finance Lease, Liability, Payment, Due [Abstract] Vesting [Axis] Vesting [Axis] Disposal Group, Disposed of by Sale, Not Discontinued Operations Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member] European Reporting Unit European Reporting Unit [Member] European Reporting Unit Total assets Total assets Assets Gain on settlement Gain (Loss) Related to Litigation Settlement Non-employee Directors Director [Member] Plan Name [Domain] Plan Name [Domain] Common stock, shares authorized (in shares) Common Stock, Shares Authorized Interest, net Interest Paid, Excluding Capitalized Interest, Operating Activities Numerator: Net Income (Loss) Attributable to Parent [Abstract] Geographical [Domain] Geographical [Domain] Title of Individual [Axis] Title of Individual [Axis] Product and Service [Domain] Product and Service [Domain] Noncontrolling Interest Noncontrolling Interest [Member] Research and engineering Research and Development Expense Accrued expenses and other current liabilities Accrued expenses and other current liabilities Accrued Expenses And Other Liabilities, Current Accrued Expenses And Other Liabilities, Current Depreciation and amortization Depreciation, Depletion and Amortization, Nonproduction Interest rate Debt Instrument, Interest Rate, Stated Percentage Schedule of Accounts Receivable, Net Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block] Less: net income attributable to noncontrolling interests, net of taxes Net Income (Loss) Attributable to Noncontrolling Interest Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Senior credit facility Revolving Credit Facility Revolving Credit Facility [Member] Revenue, remaining performance obligation, expected timing of satisfaction period Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period Net cash provided by operating activities Net Cash Provided by (Used in) Operating Activities Accounts, Notes, Loans and Financing Receivable [Line Items] Accounts, Notes, Loans and Financing Receivable [Line Items] Fair Value, Recurring and Nonrecurring [Table] Fair Value, Recurring and Nonrecurring [Table] Schedule of Components of Lease Costs and Other Information Related to Leases Lease, Cost [Table Text Block] Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Entity Tax Identification Number Entity Tax Identification Number Weighted-average discount rate Weighted Average Discount Rate, Percent [Abstract] Weighted Average Discount Rate, Percent Basic income (loss) per share Earnings Per Share, Basic [Abstract] Geographical [Axis] Geographical [Axis] Basic (in shares) Weighted-average common shares outstanding (in shares) Weighted Average Number of Shares Outstanding, Basic Segments [Domain] Segments [Domain] State and Local Jurisdiction State and Local Jurisdiction [Member] Vesting [Domain] Vesting [Domain] Percentage of reduction of rental payments Operating Lease, Percentage Of Reduction Of Rental Payments Operating Lease, Percentage Of Reduction Of Rental Payments Income taxes, net of refunds Income Taxes Paid, Net Aerospace & Defense Aerospace and Defense [Member] Aerospace and Defense Finance lease expense Lease, Cost [Abstract] Comprehensive income (loss) attributable to Mistras Group, Inc Comprehensive Income (Loss), Net of Tax, Attributable to Parent Intangible assets, net Net Carrying Amount Intangible Assets, Net (Excluding Goodwill) Net cash used in financing activities Net Cash Provided by (Used in) Financing Activities Other comprehensive income (loss): Other Comprehensive Income (Loss), Net of Tax [Abstract] Weighted-average common shares outstanding: Denominator: Weighted Average Number of Shares Outstanding, Diluted [Abstract] Deferred income taxes Deferred Income Tax Liabilities, Net Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] Basic (in dollars per share) Basic income (loss) per share (in dollars per share) Income (Loss) from Continuing Operations, Per Basic Share Schedule of Maturities of Finance Lease Liabilities Finance Lease, Liability, Fiscal Year Maturity [Table Text Block] Fair Value Measurements Fair Value Disclosures [Text Block] Performance period (years) Share Based Compensation Arrangement by Share Based Payment Award, Award Performance Period Represents the performance period of the entity, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Accounts payable Accounts Payable, Current Debt Covenant Period [Domain] Debt Covenant Period [Domain] [Domain] for Debt Covenant Period [Axis] Number or welds not in compliance Loss Contingency, Number Of Welds Alleged Not In Compliance Loss Contingency, Number Of Welds Alleged Not In Compliance Depreciation and amortization Depreciation, Depletion and Amortization Total Mistras Group, Inc. Stockholders’ Equity Parent [Member] Number of units increased (decreased) during the period (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Other Share Increase (Decrease) Accumulated other comprehensive income (loss) AOCI Attributable to Parent [Member] Inventories Increase (Decrease) in Inventories Accretion of liability Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Accretion Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Accretion Common stock, shares outstanding (in shares) Common Stock, Shares, Outstanding Software/Technology Computer Software, Intangible Asset [Member] Net settlements of restricted stock units (in shares) Stock Issued During Period, Shares, Restricted Stock Award, Net of Forfeitures Unusual or Infrequent Item, or Both [Domain] Unusual or Infrequent Item, or Both [Domain] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Depreciation Cost, Depreciation Common Stock Options Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward] Cash flows from investing activities Net Cash Provided by (Used in) Investing Activities, Continuing Operations [Abstract] Total Lease, Cost Schedule of Property, Plant and Equipment, Net Property, Plant and Equipment [Table Text Block] Equity Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract] Noncash investing and financing Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract] Increase in total number of shares authorized for issuance (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized Customer relationships Customer Relationships [Member] Litigation Loss Contingencies [Line Items] Property, Plant and Equipment, net Property, Plant and Equipment Disclosure [Text Block] Other long-term liabilities Other Liabilities, Noncurrent Schedule of Long-term Debt Schedule of Long-term Debt Instruments [Table Text Block] Debt Instrument [Line Items] Debt Instrument [Line Items] Repayment of long-term debt Repayments of Long-term Debt Earnings (loss) per common share Earnings Per Share [Abstract] Related Party Transaction [Domain] Related Party Transaction [Domain] Document Quarterly Report Document Quarterly Report Anniversary 3 Share-based Payment Arrangement, Tranche Three [Member] Outstanding at beginning of period (in dollars per share) Outstanding at end of period (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List] Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration] Oil & Gas Oil & Gas [Member] Oil & Gas Pension Related Contingencies Withdrawal from Multiemployer Defined Benefit Plan [Member] Schedule of Acquisition-related Expense Schedule of Business Combination Acquisition Related Costs [Table Text Block] Tabular disclosure of acquisition-related costs. Long-term debt, net of current portion Long-term Debt, Excluding Current Maturities Liabilities: Liabilities, Fair Value Disclosure [Abstract] Schedule of Goodwill [Table] Schedule of Goodwill [Table] Recognized share-based compensation expense Recognized share-based compensation expense (benefit) Share-based Payment Arrangement, Expense Unusual or Infrequent Item, or Both [Axis] Unusual or Infrequent Item, or Both [Axis] Europe Europe [Member] Document Fiscal Period Focus Document Fiscal Period Focus Effective income tax rate Effective Income Tax Rate Reconciliation, Percent Number of non-employee directors to whom fully vested common stock is granted Share Based Compensation Arrangement by Share Based Payment Award, Number of Non Employee Directors to whom Award is Granted Represents the number of non-employee directors to whom fully vested common stock is granted. Average share price trading period Share-based Compensation Arrangement by Share-based Payment Award, Average Share Price Trading Period Share-based Compensation Arrangement by Share-based Payment Award, Average Share Price Trading Period Net Income (loss) Net Income (loss) Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Trade accounts receivable Accounts Receivable, before Allowance for Credit Loss, Current Class Action on Behalf of State of California Class Action on Behalf Of State Of California [Member] Class Action on Behalf Of State Of California Expensed finance costs Amortization of Debt Issuance Costs Cash paid for amounts included in the measurement of lease liabilities for finance and operating leases Cash Flow, Lessee [Abstract] Cash Flow, Lessee Payables and Accruals [Abstract] Payables and Accruals [Abstract] Acquisition-related expense, net Acquisition-related expense, net Acquisition Related Costs and Fair Value Adjustments to Initial Purchase Price Allocation This element represents acquisition-related costs incurred in connection with business combinations which costs have been expensed during the period. This also includes adjustments to the fair value of the initial purchase price allocation for acquisitions including, but not limited to, changes in contingent consideration liabilities and other liabilities, accounts receivable, inventory, fixed assets, other assets, and other acquisition-related intangible assets. Acquisition-related costs also include finder's fees; advisory, legal, accounting, valuation, and other professional or consulting fees; general administrative costs, including the costs of maintaining an internal acquisitions department; and may include costs of registering and issuing debt and equity securities. Unbilled revenues accrued Contract with Customer, Asset, after Allowance for Credit Loss, Current Cash and cash equivalents at beginning of period Cash and cash equivalents at end of period Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Beginning balance (in shares) Ending balance (in shares) Shares, Issued United States UNITED STATES Common stock, par value (in dollars per share) Common Stock, Par or Stated Value Per Share Statement of Comprehensive Income [Abstract] Statement of Comprehensive Income [Abstract] Current Assets Assets, Current [Abstract] Gross Amount Finite-Lived Intangible Assets, Gross Leases [Abstract] Leases [Abstract] Entity Central Index Key Entity Central Index Key Schedule of Accrued Expenses and Other Current Liabilities Schedule of Accrued Liabilities Deferred Revenue and Contingent Consideration Liabilities Current [Table Text Block] Tabular disclosure of (a) other payables; (b) accrued liabilities; (c) deferred revenue; and (d) the fair value of contingent consideration liabilities, due within one year or within the normal operating cycle if longer. Schedule of Net Carrying Amount of Intangible Assets Schedule of Finite-Lived Intangible Assets [Table Text Block] Income Taxes Income Tax, Policy [Policy Text Block] LIBOR London Interbank Offered Rate (LIBOR) [Member] Security Exchange Name Security Exchange Name Disposal Group Classification [Domain] Disposal Group Classification [Domain] Exercised (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period Revenue Revenue from Contract with Customer [Policy Text Block] Diluted (in shares) Weighted average common shares outstanding, diluted (in shares) Weighted Average Number of Shares Outstanding, Diluted Other comprehensive gain (loss), net of tax Other Comprehensive Income (Loss), Net of Tax Requisite service period Share-based Compensation Arrangement by Share-based Payment Award, Award Requisite Service Period Denominator: Weighted Average Number of Shares Outstanding, Basic [Abstract] Related Party [Domain] Related Party [Domain] Maximum amount available for the issuance of letters of credit Line of Credit Facility Maximum Borrowing Capacity Available for Issuance of Letters of Credit Represents the maximum amount of borrowing capacity under the revolving credit facility that is available for the issuance of letters of credit. Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Current Fiscal Year End Date Current Fiscal Year End Date Schedule of Stock Option Activity Share-based Payment Arrangement, Option, Activity [Table Text Block] Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List] Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration] Floor rate Debt Instrument, Basis Spread on Variable Rate Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Finite-Lived Intangible Assets, Major Class Name [Domain] Finite-Lived Intangible Assets, Major Class Name [Domain] Net cash used in investing activities Net Cash Provided by (Used in) Investing Activities Buildings and improvements Building and Building Improvements [Member] Changes in operating assets and liabilities, net of effect of acquisitions and dispositions Increase (Decrease) in Operating Capital [Abstract] Performance condition adjustments (in dollars per share) Share-based Compensation Arrangement By Share-based Payment Award, Equity Instruments Other Than Options, Adjustments In Period, Weighted Average Grant Date Fair Value Share-based Compensation Arrangement By Share-based Payment Award, Equity Instruments Other Than Options, Adjustments In Period, Weighted Average Grant Date Fair Value Released (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value Principles of Consolidation Consolidation, Policy [Policy Text Block] Remaining balance under purchase commitment agreement Purchase Commitment, Remaining Minimum Amount Committed Total current liabilities Liabilities, Current Taxes paid related to net share settlement of share-based awards Payment, Tax Withholding, Share-based Payment Arrangement Equipment acquired through finance lease obligations Lease Obligation Incurred Finance - operating cash flows Finance Lease, Interest Payment on Liability Total consolidated leverage ratio, limit after investment in non-guarantor subsidiary Debt Instrument, Covenant Compliance, Total Consolidated Debt Leverage Ratio, After Investment In Guarantor Subsidiary Debt Instrument, Covenant Compliance, Total Consolidated Debt Leverage Ratio, After Investment In Guarantor Subsidiary Maximum borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Foreign currency translation Goodwill, Foreign Currency Translation Gain (Loss) Loss Contingencies [Table] Loss Contingencies [Table] Accrued salaries, wages and related employee benefits Accrued Salaries Wages and Employee Related Benefits Current Carrying value as of the balance sheet date of the obligations incurred through that date and payable for salaries, wages, and related employee benefit. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle, if longer). Financial information by segment Segment Reporting Information [Line Items] Entity Address, Postal Zip Code Entity Address, Postal Zip Code Extension term under agreement to purchase products from buyer Long-Term Purchase Commitment, Extension Period Long-Term Purchase Commitment, Extension Period Remainder of 2021 Finance Lease, Liability, to be Paid, Remainder of Fiscal Year Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Title of 12(b) Security Title of 12(b) Security Statement [Table] Statement [Table] Recent Accounting Pronouncements New Accounting Pronouncements, Policy [Policy Text Block] Deferred income taxes Deferred Income Tax Noncash Expense (Benefit) The noncash component of income tax expense for the period representing the increase (decrease) in the entity's deferred tax assets and liabilities pertaining to continuing operations. Cost of revenue Cost of Goods and Service, Excluding Depreciation, Depletion, and Amortization Number of proceedings Loss Contingency, New Claims Filed, Number Credit Agreement Credit Agreement [Member] Credit Agreement Statistical Measurement [Axis] Statistical Measurement [Axis] Cover [Abstract] Options fully vested (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested, Number of Shares Obligations under finance leases, net of current portion Finance Lease, Liability, Noncurrent Goodwill Balance at December 31, 2020 Balance at September 30, 2021 Goodwill Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List] Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration] Non-controlling interests Stockholders' Equity Attributable to Noncontrolling Interest Last days trading period Share-based Compensation Arrangement by Share-based Payment Award, Last Day Trading Period Share-based Compensation Arrangement by Share-based Payment Award, Last Day Trading Period Income taxes payable Accrued Income Taxes, Current Capitalized unamortized issuance cost Write off of Deferred Debt Issuance Cost Schedule of Changes in Carrying Amount of Goodwill Schedule of Goodwill [Table Text Block] Adjustments to reconcile net income (loss) to net cash provided by operating activities Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Operating lease expense Operating Lease, Cost Executive Officers Executive Officer [Member] Reversal of severance obligations Loss Contingency Accrual, Period Increase (Decrease) Schedule of Finite-Lived Intangible Assets [Table] Schedule of Finite-Lived Intangible Assets [Table] Long-Term Debt Long-term Debt [Text Block] Maximum borrowing capacity in non-U.S. Dollar currencies Line Of Credit Facility Maximum Borrowing Capacity In Non-U.S. Currencies Represents the maximum borrowing capacity in non-U.S. dollar currencies under the revolving credit facility. Debt quarterly payments Debt Instrument, Periodic Payment