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<!--XBRL Document Created with Wdesk from Workiva-->
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  <link:roleRef roleURI="http://www.xbrl.org/2009/role/negatedLabel" xlink:href="http://www.xbrl.org/lrr/role/negated-2009-12-16.xsd#negatedLabel" xlink:type="simple" />
  <link:roleRef roleURI="http://www.xbrl.org/2009/role/negatedTotalLabel" xlink:href="http://www.xbrl.org/lrr/role/negated-2009-12-16.xsd#negatedTotalLabel" xlink:type="simple" />
  <link:labelLink xlink:role="http://www.xbrl.org/2003/role/link" xlink:type="extended">
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    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_GoodwillAndIntangibleAssetsDisclosureAbstract_1D03A0D943C425E9DCF40EB895AD9EE6" xlink:to="lab_us-gaap_GoodwillAndIntangibleAssetsDisclosureAbstract_1D03A0D943C425E9DCF40EB895AD9EE6" xlink:type="arc" />
    <link:label id="lab_us-gaap_ScheduleOfGoodwillTable_6B53A91B84A5609A6EF20EB895AE38DC_terseLabel_en-US" xlink:label="lab_us-gaap_ScheduleOfGoodwillTable_6B53A91B84A5609A6EF20EB895AE38DC" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Schedule of Goodwill [Table]</link:label>
    <link:label id="lab_us-gaap_ScheduleOfGoodwillTable_6B53A91B84A5609A6EF20EB895AE38DC_label_en-US" xlink:label="lab_us-gaap_ScheduleOfGoodwillTable_6B53A91B84A5609A6EF20EB895AE38DC" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Schedule of Goodwill [Table]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfGoodwillTable" xlink:label="loc_us-gaap_ScheduleOfGoodwillTable_6B53A91B84A5609A6EF20EB895AE38DC" xlink:type="locator" />
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    <link:label id="lab_us-gaap_StatementBusinessSegmentsAxis_E5389AE09CE78F7CD5510EB895AE4EBC_terseLabel_en-US" xlink:label="lab_us-gaap_StatementBusinessSegmentsAxis_E5389AE09CE78F7CD5510EB895AE4EBC" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Segments [Axis]</link:label>
    <link:label id="lab_us-gaap_StatementBusinessSegmentsAxis_E5389AE09CE78F7CD5510EB895AE4EBC_label_en-US" xlink:label="lab_us-gaap_StatementBusinessSegmentsAxis_E5389AE09CE78F7CD5510EB895AE4EBC" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Segments [Axis]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementBusinessSegmentsAxis" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_E5389AE09CE78F7CD5510EB895AE4EBC" xlink:type="locator" />
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    <link:label id="lab_us-gaap_SegmentDomain_F9CFB10BCC08A4A962660EB895AEE192_terseLabel_en-US" xlink:label="lab_us-gaap_SegmentDomain_F9CFB10BCC08A4A962660EB895AEE192" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Segments [Domain]</link:label>
    <link:label id="lab_us-gaap_SegmentDomain_F9CFB10BCC08A4A962660EB895AEE192_label_en-US" xlink:label="lab_us-gaap_SegmentDomain_F9CFB10BCC08A4A962660EB895AEE192" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Segments [Domain]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SegmentDomain" xlink:label="loc_us-gaap_SegmentDomain_F9CFB10BCC08A4A962660EB895AEE192" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_SegmentDomain_F9CFB10BCC08A4A962660EB895AEE192" xlink:to="lab_us-gaap_SegmentDomain_F9CFB10BCC08A4A962660EB895AEE192" xlink:type="arc" />
    <link:label id="lab_mg_ServicesMember_C326279A9D531010FBC40EB895AF2A4B_terseLabel_en-US" xlink:label="lab_mg_ServicesMember_C326279A9D531010FBC40EB895AF2A4B" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Services</link:label>
    <link:label id="lab_mg_ServicesMember_C326279A9D531010FBC40EB895AF2A4B_label_en-US" xlink:label="lab_mg_ServicesMember_C326279A9D531010FBC40EB895AF2A4B" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Services [Member]</link:label>
    <link:label id="lab_mg_ServicesMember_C326279A9D531010FBC40EB895AF2A4B_documentation_en-US" xlink:label="lab_mg_ServicesMember_C326279A9D531010FBC40EB895AF2A4B" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Represents Services, a business segment of the entity.</link:label>
    <link:loc xlink:href="mg-20181231.xsd#mg_ServicesMember" xlink:label="loc_mg_ServicesMember_C326279A9D531010FBC40EB895AF2A4B" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_mg_ServicesMember_C326279A9D531010FBC40EB895AF2A4B" xlink:to="lab_mg_ServicesMember_C326279A9D531010FBC40EB895AF2A4B" xlink:type="arc" />
    <link:label id="lab_mg_InternationalMember_4A4B0B2B1305D09BE0BF0EB895AFBB13_terseLabel_en-US" xlink:label="lab_mg_InternationalMember_4A4B0B2B1305D09BE0BF0EB895AFBB13" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">International</link:label>
    <link:label id="lab_mg_InternationalMember_4A4B0B2B1305D09BE0BF0EB895AFBB13_label_en-US" xlink:label="lab_mg_InternationalMember_4A4B0B2B1305D09BE0BF0EB895AFBB13" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">International [Member]</link:label>
    <link:label id="lab_mg_InternationalMember_4A4B0B2B1305D09BE0BF0EB895AFBB13_documentation_en-US" xlink:label="lab_mg_InternationalMember_4A4B0B2B1305D09BE0BF0EB895AFBB13" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Represents International, a business segment of the entity.</link:label>
    <link:loc xlink:href="mg-20181231.xsd#mg_InternationalMember" xlink:label="loc_mg_InternationalMember_4A4B0B2B1305D09BE0BF0EB895AFBB13" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_mg_InternationalMember_4A4B0B2B1305D09BE0BF0EB895AFBB13" xlink:to="lab_mg_InternationalMember_4A4B0B2B1305D09BE0BF0EB895AFBB13" xlink:type="arc" />
    <link:label id="lab_mg_ProductsandSystemsMember_9C483D11E6037B812E6A0EB895AFA15E_terseLabel_en-US" xlink:label="lab_mg_ProductsandSystemsMember_9C483D11E6037B812E6A0EB895AFA15E" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Products and Systems</link:label>
    <link:label id="lab_mg_ProductsandSystemsMember_9C483D11E6037B812E6A0EB895AFA15E_label_en-US" xlink:label="lab_mg_ProductsandSystemsMember_9C483D11E6037B812E6A0EB895AFA15E" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Products and Systems [Member]</link:label>
    <link:label id="lab_mg_ProductsandSystemsMember_9C483D11E6037B812E6A0EB895AFA15E_documentation_en-US" xlink:label="lab_mg_ProductsandSystemsMember_9C483D11E6037B812E6A0EB895AFA15E" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Products and Systems</link:label>
    <link:loc xlink:href="mg-20181231.xsd#mg_ProductsandSystemsMember" xlink:label="loc_mg_ProductsandSystemsMember_9C483D11E6037B812E6A0EB895AFA15E" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_mg_ProductsandSystemsMember_9C483D11E6037B812E6A0EB895AFA15E" xlink:to="lab_mg_ProductsandSystemsMember_9C483D11E6037B812E6A0EB895AFA15E" xlink:type="arc" />
    <link:label id="lab_us-gaap_GoodwillLineItems_89BFC73024DAD5CE139C0EB895AF7D82_terseLabel_en-US" xlink:label="lab_us-gaap_GoodwillLineItems_89BFC73024DAD5CE139C0EB895AF7D82" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Goodwill</link:label>
    <link:label id="lab_us-gaap_GoodwillLineItems_89BFC73024DAD5CE139C0EB895AF7D82_label_en-US" xlink:label="lab_us-gaap_GoodwillLineItems_89BFC73024DAD5CE139C0EB895AF7D82" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Goodwill [Line Items]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_GoodwillLineItems" xlink:label="loc_us-gaap_GoodwillLineItems_89BFC73024DAD5CE139C0EB895AF7D82" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_GoodwillLineItems_89BFC73024DAD5CE139C0EB895AF7D82" xlink:to="lab_us-gaap_GoodwillLineItems_89BFC73024DAD5CE139C0EB895AF7D82" xlink:type="arc" />
    <link:label id="lab_us-gaap_GoodwillRollForward_A857665EA35B96772D5A0EB895AF538F_terseLabel_en-US" xlink:label="lab_us-gaap_GoodwillRollForward_A857665EA35B96772D5A0EB895AF538F" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Changes in the carrying amount of goodwill</link:label>
    <link:label id="lab_us-gaap_GoodwillRollForward_A857665EA35B96772D5A0EB895AF538F_label_en-US" xlink:label="lab_us-gaap_GoodwillRollForward_A857665EA35B96772D5A0EB895AF538F" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Goodwill [Roll Forward]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_GoodwillRollForward" xlink:label="loc_us-gaap_GoodwillRollForward_A857665EA35B96772D5A0EB895AF538F" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_GoodwillRollForward_A857665EA35B96772D5A0EB895AF538F" xlink:to="lab_us-gaap_GoodwillRollForward_A857665EA35B96772D5A0EB895AF538F" xlink:type="arc" />
    <link:label id="lab_us-gaap_Goodwill_26999409BC8E39A040F30EB895B0AF02_periodStartLabel_en-US" xlink:label="lab_us-gaap_Goodwill_26999409BC8E39A040F30EB895B0AF02" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel" xlink:type="resource" xml:lang="en-US">Balance at the beginning of the period</link:label>
    <link:label id="lab_us-gaap_Goodwill_26999409BC8E39A040F30EB895B0AF02_label_en-US" xlink:label="lab_us-gaap_Goodwill_26999409BC8E39A040F30EB895B0AF02" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Goodwill</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_Goodwill" xlink:label="loc_us-gaap_Goodwill_26999409BC8E39A040F30EB895B0AF02" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_Goodwill_26999409BC8E39A040F30EB895B0AF02" xlink:to="lab_us-gaap_Goodwill_26999409BC8E39A040F30EB895B0AF02" xlink:type="arc" />
    <link:label id="lab_us-gaap_GoodwillAcquiredDuringPeriod_C73C438E1CAD5BB3C7640EE86DE50D9E_terseLabel_en-US" xlink:label="lab_us-gaap_GoodwillAcquiredDuringPeriod_C73C438E1CAD5BB3C7640EE86DE50D9E" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Goodwill acquired during the year</link:label>
    <link:label id="lab_us-gaap_GoodwillAcquiredDuringPeriod_C73C438E1CAD5BB3C7640EE86DE50D9E_label_en-US" xlink:label="lab_us-gaap_GoodwillAcquiredDuringPeriod_C73C438E1CAD5BB3C7640EE86DE50D9E" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Goodwill, Acquired During Period</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_GoodwillAcquiredDuringPeriod" xlink:label="loc_us-gaap_GoodwillAcquiredDuringPeriod_C73C438E1CAD5BB3C7640EE86DE50D9E" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_GoodwillAcquiredDuringPeriod_C73C438E1CAD5BB3C7640EE86DE50D9E" xlink:to="lab_us-gaap_GoodwillAcquiredDuringPeriod_C73C438E1CAD5BB3C7640EE86DE50D9E" xlink:type="arc" />
    <link:label id="lab_us-gaap_GoodwillImpairmentLoss_5BCB0F61C047302DD5E20EB895B060E6_negatedTerseLabel_en-US" xlink:label="lab_us-gaap_GoodwillImpairmentLoss_5BCB0F61C047302DD5E20EB895B060E6" xlink:role="http://www.xbrl.org/2009/role/negatedTerseLabel" xlink:type="resource" xml:lang="en-US">Impairment charge</link:label>
    <link:label id="lab_us-gaap_GoodwillImpairmentLoss_5BCB0F61C047302DD5E20EB895B060E6_label_en-US" xlink:label="lab_us-gaap_GoodwillImpairmentLoss_5BCB0F61C047302DD5E20EB895B060E6" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Goodwill, Impairment Loss</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_GoodwillImpairmentLoss" xlink:label="loc_us-gaap_GoodwillImpairmentLoss_5BCB0F61C047302DD5E20EB895B060E6" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_GoodwillImpairmentLoss_5BCB0F61C047302DD5E20EB895B060E6" xlink:to="lab_us-gaap_GoodwillImpairmentLoss_5BCB0F61C047302DD5E20EB895B060E6" xlink:type="arc" />
    <link:label id="lab_us-gaap_GoodwillPurchaseAccountingAdjustments_0AFF01B6E2F47C02115B0EB895B03D33_terseLabel_en-US" xlink:label="lab_us-gaap_GoodwillPurchaseAccountingAdjustments_0AFF01B6E2F47C02115B0EB895B03D33" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Adjustments to preliminary purchase price allocations</link:label>
    <link:label id="lab_us-gaap_GoodwillPurchaseAccountingAdjustments_0AFF01B6E2F47C02115B0EB895B03D33_label_en-US" xlink:label="lab_us-gaap_GoodwillPurchaseAccountingAdjustments_0AFF01B6E2F47C02115B0EB895B03D33" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Goodwill, Purchase Accounting Adjustments</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_GoodwillPurchaseAccountingAdjustments" xlink:label="loc_us-gaap_GoodwillPurchaseAccountingAdjustments_0AFF01B6E2F47C02115B0EB895B03D33" xlink:type="locator" />
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    <link:label id="lab_us-gaap_GoodwillForeignCurrencyTranslationGainLoss_72EBED66719EF5DAF1410EB895B14E3B_terseLabel_en-US" xlink:label="lab_us-gaap_GoodwillForeignCurrencyTranslationGainLoss_72EBED66719EF5DAF1410EB895B14E3B" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Foreign currency translation</link:label>
    <link:label id="lab_us-gaap_GoodwillForeignCurrencyTranslationGainLoss_72EBED66719EF5DAF1410EB895B14E3B_label_en-US" xlink:label="lab_us-gaap_GoodwillForeignCurrencyTranslationGainLoss_72EBED66719EF5DAF1410EB895B14E3B" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Goodwill, Foreign Currency Translation Gain (Loss)</link:label>
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    <link:label id="lab_us-gaap_Goodwill_9219570F810DBE68A6DB0EB895B1C056_periodEndLabel_en-US" xlink:label="lab_us-gaap_Goodwill_9219570F810DBE68A6DB0EB895B1C056" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel" xlink:type="resource" xml:lang="en-US">Balance at the end of the period</link:label>
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    <link:label id="lab_us-gaap_WithdrawalFromMultiemployerDefinedBenefitPlanMember_8953828D3E704DF356086042D8ED02D5_terseLabel_en-US" xlink:label="lab_us-gaap_WithdrawalFromMultiemployerDefinedBenefitPlanMember_8953828D3E704DF356086042D8ED02D5" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Pension related contingencies</link:label>
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    <link:label id="lab_us-gaap_RelatedPartyDomain_9CEA0FFDA0693CD17B6E6042D8EDC0D7_label_en-US" xlink:label="lab_us-gaap_RelatedPartyDomain_9CEA0FFDA0693CD17B6E6042D8EDC0D7" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Related Party [Domain]</link:label>
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    <link:label id="lab_us-gaap_LitigationCaseTypeDomain_CCDCFD7455E855AE7FFC6042D8ED7331_terseLabel_en-US" xlink:label="lab_us-gaap_LitigationCaseTypeDomain_CCDCFD7455E855AE7FFC6042D8ED7331" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Litigation Case [Domain]</link:label>
    <link:label id="lab_us-gaap_LitigationCaseTypeDomain_CCDCFD7455E855AE7FFC6042D8ED7331_label_en-US" xlink:label="lab_us-gaap_LitigationCaseTypeDomain_CCDCFD7455E855AE7FFC6042D8ED7331" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Litigation Case [Domain]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LitigationCaseTypeDomain" xlink:label="loc_us-gaap_LitigationCaseTypeDomain_CCDCFD7455E855AE7FFC6042D8ED7331" xlink:type="locator" />
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    <link:label id="lab_mg_AGLServicesCompanyvMistrasGroupMember_C593EEB8592387DE7A496042D8ED2A81_terseLabel_en-US" xlink:label="lab_mg_AGLServicesCompanyvMistrasGroupMember_C593EEB8592387DE7A496042D8ED2A81" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">AGL Services Company v Mistras Group, Inc.</link:label>
    <link:label id="lab_mg_AGLServicesCompanyvMistrasGroupMember_C593EEB8592387DE7A496042D8ED2A81_label_en-US" xlink:label="lab_mg_AGLServicesCompanyvMistrasGroupMember_C593EEB8592387DE7A496042D8ED2A81" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">AGL Services Company v Mistras Group [Member]</link:label>
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    <link:label id="lab_mg_TriumphAerostructuresVoughtAircraftDivisionvMistrasGroupMember_96371B2C291F2120702D6042D8ED5317_terseLabel_en-US" xlink:label="lab_mg_TriumphAerostructuresVoughtAircraftDivisionvMistrasGroupMember_96371B2C291F2120702D6042D8ED5317" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Triumph Aerostructures-Vought Aircraft Division v Mistras Group, Inc.</link:label>
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    <link:label id="lab_mg_TriumphAerostructuresVoughtAircraftDivisionvMistrasGroupMember_96371B2C291F2120702D6042D8ED5317_documentation_en-US" xlink:label="lab_mg_TriumphAerostructuresVoughtAircraftDivisionvMistrasGroupMember_96371B2C291F2120702D6042D8ED5317" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Triumph Aerostructures-Vought Aircraft Division v Mistras Group</link:label>
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    <link:label id="lab_mg_McAllisterv.MistrasGroupIncMember_CB9EDAD27B267F5F1F526042D8EDE6BE_terseLabel_en-US" xlink:label="lab_mg_McAllisterv.MistrasGroupIncMember_CB9EDAD27B267F5F1F526042D8EDE6BE" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">McAllister v. Mistras Group, Inc.</link:label>
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    <link:label id="lab_us-gaap_LitigationSettlementAmountAwardedToOtherParty_944D99A91759538C641E6042D8ED7140_terseLabel_en-US" xlink:label="lab_us-gaap_LitigationSettlementAmountAwardedToOtherParty_944D99A91759538C641E6042D8ED7140" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Litigation settlement amount</link:label>
    <link:label id="lab_us-gaap_LitigationSettlementAmountAwardedToOtherParty_944D99A91759538C641E6042D8ED7140_label_en-US" xlink:label="lab_us-gaap_LitigationSettlementAmountAwardedToOtherParty_944D99A91759538C641E6042D8ED7140" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Litigation Settlement, Amount Awarded to Other Party</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LitigationSettlementAmountAwardedToOtherParty" xlink:label="loc_us-gaap_LitigationSettlementAmountAwardedToOtherParty_944D99A91759538C641E6042D8ED7140" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LitigationSettlementAmountAwardedToOtherParty_944D99A91759538C641E6042D8ED7140" xlink:to="lab_us-gaap_LitigationSettlementAmountAwardedToOtherParty_944D99A91759538C641E6042D8ED7140" xlink:type="arc" />
    <link:label id="lab_us-gaap_LossContingencyDamagesSoughtValue_245C7EBB991BF83D9E376042D8ED1B42_terseLabel_en-US" xlink:label="lab_us-gaap_LossContingencyDamagesSoughtValue_245C7EBB991BF83D9E376042D8ED1B42" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Verbal demand for damages</link:label>
    <link:label id="lab_us-gaap_LossContingencyDamagesSoughtValue_245C7EBB991BF83D9E376042D8ED1B42_label_en-US" xlink:label="lab_us-gaap_LossContingencyDamagesSoughtValue_245C7EBB991BF83D9E376042D8ED1B42" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Loss Contingency, Damages Sought, Value</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LossContingencyDamagesSoughtValue" xlink:label="loc_us-gaap_LossContingencyDamagesSoughtValue_245C7EBB991BF83D9E376042D8ED1B42" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LossContingencyDamagesSoughtValue_245C7EBB991BF83D9E376042D8ED1B42" xlink:to="lab_us-gaap_LossContingencyDamagesSoughtValue_245C7EBB991BF83D9E376042D8ED1B42" xlink:type="arc" />
    <link:label id="lab_us-gaap_LitigationSettlementExpense_99F3445BC47455FA76626042D8EDD504_verboseLabel_en-US" xlink:label="lab_us-gaap_LitigationSettlementExpense_99F3445BC47455FA76626042D8EDD504" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:type="resource" xml:lang="en-US">Legal settlement charges</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LitigationSettlementExpense" xlink:label="loc_us-gaap_LitigationSettlementExpense_99F3445BC47455FA76626042D8EDD504" xlink:type="locator" />
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    <link:label id="lab_us-gaap_LossContingencyNewClaimsFiledNumber_90838D18C3455ACC24B66042D8EDCC55_terseLabel_en-US" xlink:label="lab_us-gaap_LossContingencyNewClaimsFiledNumber_90838D18C3455ACC24B66042D8EDCC55" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Number of claims filed</link:label>
    <link:label id="lab_us-gaap_LossContingencyNewClaimsFiledNumber_90838D18C3455ACC24B66042D8EDCC55_label_en-US" xlink:label="lab_us-gaap_LossContingencyNewClaimsFiledNumber_90838D18C3455ACC24B66042D8EDCC55" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Loss Contingency, New Claims Filed, Number</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LossContingencyNewClaimsFiledNumber" xlink:label="loc_us-gaap_LossContingencyNewClaimsFiledNumber_90838D18C3455ACC24B66042D8EDCC55" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LossContingencyNewClaimsFiledNumber_90838D18C3455ACC24B66042D8EDCC55" xlink:to="lab_us-gaap_LossContingencyNewClaimsFiledNumber_90838D18C3455ACC24B66042D8EDCC55" xlink:type="arc" />
    <link:label id="lab_us-gaap_LossContingencyAccrualAtCarryingValue_56D3AC9D4BEE9F8DECCA60498A87DEB0_verboseLabel_en-US" xlink:label="lab_us-gaap_LossContingencyAccrualAtCarryingValue_56D3AC9D4BEE9F8DECCA60498A87DEB0" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:type="resource" xml:lang="en-US">Potential withdrawal liability related to withdrawal from multiemployer pension plans</link:label>
    <link:label id="lab_us-gaap_LossContingencyAccrualAtCarryingValue_56D3AC9D4BEE9F8DECCA60498A87DEB0_label_en-US" xlink:label="lab_us-gaap_LossContingencyAccrualAtCarryingValue_56D3AC9D4BEE9F8DECCA60498A87DEB0" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Loss Contingency Accrual</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LossContingencyAccrualAtCarryingValue" xlink:label="loc_us-gaap_LossContingencyAccrualAtCarryingValue_56D3AC9D4BEE9F8DECCA60498A87DEB0" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LossContingencyAccrualAtCarryingValue_56D3AC9D4BEE9F8DECCA60498A87DEB0" xlink:to="lab_us-gaap_LossContingencyAccrualAtCarryingValue_56D3AC9D4BEE9F8DECCA60498A87DEB0" xlink:type="arc" />
    <link:label id="lab_us-gaap_LossContingencyLossInPeriod_953D8357749EDF22AFF86042D8ED8C17_terseLabel_en-US" xlink:label="lab_us-gaap_LossContingencyLossInPeriod_953D8357749EDF22AFF86042D8ED8C17" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Contingency related charges</link:label>
    <link:label id="lab_us-gaap_LossContingencyLossInPeriod_953D8357749EDF22AFF86042D8ED8C17_label_en-US" xlink:label="lab_us-gaap_LossContingencyLossInPeriod_953D8357749EDF22AFF86042D8ED8C17" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Loss Contingency, Loss in Period</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LossContingencyLossInPeriod" xlink:label="loc_us-gaap_LossContingencyLossInPeriod_953D8357749EDF22AFF86042D8ED8C17" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LossContingencyLossInPeriod_953D8357749EDF22AFF86042D8ED8C17" xlink:to="lab_us-gaap_LossContingencyLossInPeriod_953D8357749EDF22AFF86042D8ED8C17" xlink:type="arc" />
    <link:label id="lab_mg_TemporaryStaffLeasingContractPeriod_FB7295116CB3B70E07C46042D8EDB355_terseLabel_en-US" xlink:label="lab_mg_TemporaryStaffLeasingContractPeriod_FB7295116CB3B70E07C46042D8EDB355" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Period covered by temporary staff leasing contract</link:label>
    <link:label id="lab_mg_TemporaryStaffLeasingContractPeriod_FB7295116CB3B70E07C46042D8EDB355_label_en-US" xlink:label="lab_mg_TemporaryStaffLeasingContractPeriod_FB7295116CB3B70E07C46042D8EDB355" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Temporary Staff Leasing Contract Period</link:label>
    <link:label id="lab_mg_TemporaryStaffLeasingContractPeriod_FB7295116CB3B70E07C46042D8EDB355_documentation_en-US" xlink:label="lab_mg_TemporaryStaffLeasingContractPeriod_FB7295116CB3B70E07C46042D8EDB355" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Temporary Staff Leasing Contract Period</link:label>
    <link:loc xlink:href="mg-20181231.xsd#mg_TemporaryStaffLeasingContractPeriod" xlink:label="loc_mg_TemporaryStaffLeasingContractPeriod_FB7295116CB3B70E07C46042D8EDB355" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_mg_TemporaryStaffLeasingContractPeriod_FB7295116CB3B70E07C46042D8EDB355" xlink:to="lab_mg_TemporaryStaffLeasingContractPeriod_FB7295116CB3B70E07C46042D8EDB355" xlink:type="arc" />
    <link:label id="lab_mg_NumberofEmployeesUnderCurrentStaffLeasingContracts_F2DCD6680D212EF3DC7E6042D8EDD7B0_terseLabel_en-US" xlink:label="lab_mg_NumberofEmployeesUnderCurrentStaffLeasingContracts_F2DCD6680D212EF3DC7E6042D8EDD7B0" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Number of employees under staff leasing contract</link:label>
    <link:label id="lab_mg_NumberofEmployeesUnderCurrentStaffLeasingContracts_F2DCD6680D212EF3DC7E6042D8EDD7B0_label_en-US" xlink:label="lab_mg_NumberofEmployeesUnderCurrentStaffLeasingContracts_F2DCD6680D212EF3DC7E6042D8EDD7B0" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Number of Employees Under Current Staff Leasing Contracts</link:label>
    <link:label id="lab_mg_NumberofEmployeesUnderCurrentStaffLeasingContracts_F2DCD6680D212EF3DC7E6042D8EDD7B0_documentation_en-US" xlink:label="lab_mg_NumberofEmployeesUnderCurrentStaffLeasingContracts_F2DCD6680D212EF3DC7E6042D8EDD7B0" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Number of Employees Under Current Staff Leasing Contracts</link:label>
    <link:loc xlink:href="mg-20181231.xsd#mg_NumberofEmployeesUnderCurrentStaffLeasingContracts" xlink:label="loc_mg_NumberofEmployeesUnderCurrentStaffLeasingContracts_F2DCD6680D212EF3DC7E6042D8EDD7B0" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_mg_NumberofEmployeesUnderCurrentStaffLeasingContracts_F2DCD6680D212EF3DC7E6042D8EDD7B0" xlink:to="lab_mg_NumberofEmployeesUnderCurrentStaffLeasingContracts_F2DCD6680D212EF3DC7E6042D8EDD7B0" xlink:type="arc" />
    <link:label id="lab_us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueLow_16682B1462F994E5B6806042D8ED173A_terseLabel_en-US" xlink:label="lab_us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueLow_16682B1462F994E5B6806042D8ED173A" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Potential acquisition-related contingent consideration, low end of range</link:label>
    <link:label id="lab_us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueLow_16682B1462F994E5B6806042D8ED173A_label_en-US" xlink:label="lab_us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueLow_16682B1462F994E5B6806042D8ED173A" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, Low</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueLow" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueLow_16682B1462F994E5B6806042D8ED173A" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueLow_16682B1462F994E5B6806042D8ED173A" xlink:to="lab_us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueLow_16682B1462F994E5B6806042D8ED173A" xlink:type="arc" />
    <link:label id="lab_us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh_A34B842A521B6CB3EBBE6042D8EDA026_terseLabel_en-US" xlink:label="lab_us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh_A34B842A521B6CB3EBBE6042D8EDA026" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Potential acquisition-related contingent consideration, high end of range</link:label>
    <link:label id="lab_us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh_A34B842A521B6CB3EBBE6042D8EDA026_label_en-US" xlink:label="lab_us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh_A34B842A521B6CB3EBBE6042D8EDA026" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh_A34B842A521B6CB3EBBE6042D8EDA026" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh_A34B842A521B6CB3EBBE6042D8EDA026" xlink:to="lab_us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh_A34B842A521B6CB3EBBE6042D8EDA026" xlink:type="arc" />
    <link:label id="lab_mg_BusinessCombinationContingentConsiderationPaymentPeriod_8E6A93615E7F62136CBE6042D8ED0285_terseLabel_en-US" xlink:label="lab_mg_BusinessCombinationContingentConsiderationPaymentPeriod_8E6A93615E7F62136CBE6042D8ED0285" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Period over which potential acquisition-related contingent consideration would be payable</link:label>
    <link:label id="lab_mg_BusinessCombinationContingentConsiderationPaymentPeriod_8E6A93615E7F62136CBE6042D8ED0285_label_en-US" xlink:label="lab_mg_BusinessCombinationContingentConsiderationPaymentPeriod_8E6A93615E7F62136CBE6042D8ED0285" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Business Combination, Contingent Consideration Payment Period</link:label>
    <link:label id="lab_mg_BusinessCombinationContingentConsiderationPaymentPeriod_8E6A93615E7F62136CBE6042D8ED0285_documentation_en-US" xlink:label="lab_mg_BusinessCombinationContingentConsiderationPaymentPeriod_8E6A93615E7F62136CBE6042D8ED0285" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Represents the period over which the expected contingent consideration would be payable by the entity based on achievement of specific performance metrics by certain of the acquired companies.</link:label>
    <link:loc xlink:href="mg-20181231.xsd#mg_BusinessCombinationContingentConsiderationPaymentPeriod" xlink:label="loc_mg_BusinessCombinationContingentConsiderationPaymentPeriod_8E6A93615E7F62136CBE6042D8ED0285" xlink:type="locator" />
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    <link:label id="lab_us-gaap_PerformanceSharesMember_38B23AC39434412279E66042D97A06BA_terseLabel_en-US" xlink:label="lab_us-gaap_PerformanceSharesMember_38B23AC39434412279E66042D97A06BA" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">PRSUs</link:label>
    <link:label id="lab_us-gaap_PerformanceSharesMember_38B23AC39434412279E66042D97A06BA_label_en-US" xlink:label="lab_us-gaap_PerformanceSharesMember_38B23AC39434412279E66042D97A06BA" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Performance Shares [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PerformanceSharesMember" xlink:label="loc_us-gaap_PerformanceSharesMember_38B23AC39434412279E66042D97A06BA" xlink:type="locator" />
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    <link:label id="lab_mg_PerformanceSharesWithOneYearEPSPerformanceConditionMember_4F6D93D01244670B515B6042D97ADD3F_terseLabel_en-US" xlink:label="lab_mg_PerformanceSharesWithOneYearEPSPerformanceConditionMember_4F6D93D01244670B515B6042D97ADD3F" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">PRSUs with one year performance condition</link:label>
    <link:label id="lab_mg_PerformanceSharesWithOneYearEPSPerformanceConditionMember_4F6D93D01244670B515B6042D97ADD3F_label_en-US" xlink:label="lab_mg_PerformanceSharesWithOneYearEPSPerformanceConditionMember_4F6D93D01244670B515B6042D97ADD3F" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Performance Shares with One Year EPS Performance Condition [Member]</link:label>
    <link:label id="lab_mg_PerformanceSharesWithOneYearEPSPerformanceConditionMember_4F6D93D01244670B515B6042D97ADD3F_documentation_en-US" xlink:label="lab_mg_PerformanceSharesWithOneYearEPSPerformanceConditionMember_4F6D93D01244670B515B6042D97ADD3F" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Represents information pertaining to performance shares with one year EPS performance condition.</link:label>
    <link:loc xlink:href="mg-20181231.xsd#mg_PerformanceSharesWithOneYearEPSPerformanceConditionMember" xlink:label="loc_mg_PerformanceSharesWithOneYearEPSPerformanceConditionMember_4F6D93D01244670B515B6042D97ADD3F" xlink:type="locator" />
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    <link:label id="lab_mg_PerformanceSharesWithTwoYearEPSPerformanceConditionMember_A185B752AB06F7F00B566042D97A5362_terseLabel_en-US" xlink:label="lab_mg_PerformanceSharesWithTwoYearEPSPerformanceConditionMember_A185B752AB06F7F00B566042D97A5362" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">PRSUs with two year performance condition</link:label>
    <link:label id="lab_mg_PerformanceSharesWithTwoYearEPSPerformanceConditionMember_A185B752AB06F7F00B566042D97A5362_label_en-US" xlink:label="lab_mg_PerformanceSharesWithTwoYearEPSPerformanceConditionMember_A185B752AB06F7F00B566042D97A5362" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Performance Shares with Two Year EPS Performance Condition [Member]</link:label>
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    <link:label id="lab_us-gaap_AwardDateDomain_A391C955AA6434994D296042D97A8020_label_en-US" xlink:label="lab_us-gaap_AwardDateDomain_A391C955AA6434994D296042D97A8020" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Award Date [Domain]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AwardDateDomain" xlink:label="loc_us-gaap_AwardDateDomain_A391C955AA6434994D296042D97A8020" xlink:type="locator" />
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    <link:label id="lab_mg_Fiscal2014GrantsMember_327D1CC46E299CE21CA36042D97ABE2A_documentation_en-US" xlink:label="lab_mg_Fiscal2014GrantsMember_327D1CC46E299CE21CA36042D97ABE2A" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Fiscal 2014 Grants [Member]</link:label>
    <link:loc xlink:href="mg-20181231.xsd#mg_Fiscal2014GrantsMember" xlink:label="loc_mg_Fiscal2014GrantsMember_327D1CC46E299CE21CA36042D97ABE2A" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_mg_Fiscal2014GrantsMember_327D1CC46E299CE21CA36042D97ABE2A" xlink:to="lab_mg_Fiscal2014GrantsMember_327D1CC46E299CE21CA36042D97ABE2A" xlink:type="arc" />
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    <link:loc xlink:href="mg-20181231.xsd#mg_Fiscal2015GrantsMember" xlink:label="loc_mg_Fiscal2015GrantsMember_8CBEB5194E61161F3BB96042D97A8182" xlink:type="locator" />
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    <link:loc xlink:href="mg-20181231.xsd#mg_Fiscal2016GrantsMember" xlink:label="loc_mg_Fiscal2016GrantsMember_4071DBC7126344B815C96042D97A638A" xlink:type="locator" />
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    <link:label id="lab_us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_B7AFBB13466E5996715C6042D97A4155_label_en-US" xlink:label="lab_us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_B7AFBB13466E5996715C6042D97A4155" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Relationship to Entity [Domain]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TitleOfIndividualWithRelationshipToEntityDomain" xlink:label="loc_us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_B7AFBB13466E5996715C6042D97A4155" xlink:type="locator" />
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    <link:label id="lab_mg_ExecutiveAndSeniorOfficersMember_EF844FBC6B5D2DCF7BDA6042D97AF0F1_terseLabel_en-US" xlink:label="lab_mg_ExecutiveAndSeniorOfficersMember_EF844FBC6B5D2DCF7BDA6042D97AF0F1" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Executive and senior officers</link:label>
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    <link:label id="lab_mg_ExecutiveAndSeniorOfficersMember_EF844FBC6B5D2DCF7BDA6042D97AF0F1_documentation_en-US" xlink:label="lab_mg_ExecutiveAndSeniorOfficersMember_EF844FBC6B5D2DCF7BDA6042D97AF0F1" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Represents information pertaining to the executives and senior officers of the reporting entity.</link:label>
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    <link:label id="lab_us-gaap_VestingAxis_220CEEACBF76C52DCC036042D97A773D_terseLabel_en-US" xlink:label="lab_us-gaap_VestingAxis_220CEEACBF76C52DCC036042D97A773D" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Vesting [Axis]</link:label>
    <link:label id="lab_us-gaap_VestingAxis_220CEEACBF76C52DCC036042D97A773D_label_en-US" xlink:label="lab_us-gaap_VestingAxis_220CEEACBF76C52DCC036042D97A773D" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Vesting [Axis]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_VestingAxis" xlink:label="loc_us-gaap_VestingAxis_220CEEACBF76C52DCC036042D97A773D" xlink:type="locator" />
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    <link:label id="lab_us-gaap_VestingDomain_C972E589996FFF9F84BF6042D97ADC2D_terseLabel_en-US" xlink:label="lab_us-gaap_VestingDomain_C972E589996FFF9F84BF6042D97ADC2D" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Vesting [Domain]</link:label>
    <link:label id="lab_us-gaap_VestingDomain_C972E589996FFF9F84BF6042D97ADC2D_label_en-US" xlink:label="lab_us-gaap_VestingDomain_C972E589996FFF9F84BF6042D97ADC2D" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Vesting [Domain]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_VestingDomain" xlink:label="loc_us-gaap_VestingDomain_C972E589996FFF9F84BF6042D97ADC2D" xlink:type="locator" />
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    <link:label id="lab_us-gaap_ShareBasedCompensationAwardTrancheOneMember_34433143CCB057DD4DA26042D97A24B2_terseLabel_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationAwardTrancheOneMember_34433143CCB057DD4DA26042D97A24B2" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">1st Anniversary</link:label>
    <link:label id="lab_us-gaap_ShareBasedCompensationAwardTrancheOneMember_34433143CCB057DD4DA26042D97A24B2_label_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationAwardTrancheOneMember_34433143CCB057DD4DA26042D97A24B2" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Share-based Compensation Award, Tranche One [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationAwardTrancheOneMember" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_34433143CCB057DD4DA26042D97A24B2" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_34433143CCB057DD4DA26042D97A24B2" xlink:to="lab_us-gaap_ShareBasedCompensationAwardTrancheOneMember_34433143CCB057DD4DA26042D97A24B2" xlink:type="arc" />
    <link:label id="lab_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_C81BAE17ACCA689BAD5D6042D97AD741_terseLabel_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_C81BAE17ACCA689BAD5D6042D97AD741" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">2nd Anniversary</link:label>
    <link:label id="lab_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_C81BAE17ACCA689BAD5D6042D97AD741_label_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_C81BAE17ACCA689BAD5D6042D97AD741" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Share-based Compensation Award, Tranche Two [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationAwardTrancheTwoMember" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_C81BAE17ACCA689BAD5D6042D97AD741" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_C81BAE17ACCA689BAD5D6042D97AD741" xlink:to="lab_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_C81BAE17ACCA689BAD5D6042D97AD741" xlink:type="arc" />
    <link:label id="lab_us-gaap_ShareBasedCompensationAwardTrancheThreeMember_C7719C55539034FE4E546042D97A6F4B_terseLabel_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationAwardTrancheThreeMember_C7719C55539034FE4E546042D97A6F4B" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">3rd Anniversary</link:label>
    <link:label id="lab_us-gaap_ShareBasedCompensationAwardTrancheThreeMember_C7719C55539034FE4E546042D97A6F4B_label_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationAwardTrancheThreeMember_C7719C55539034FE4E546042D97A6F4B" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Share-based Compensation Award, Tranche Three [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationAwardTrancheThreeMember" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheThreeMember_C7719C55539034FE4E546042D97A6F4B" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ShareBasedCompensationAwardTrancheThreeMember_C7719C55539034FE4E546042D97A6F4B" xlink:to="lab_us-gaap_ShareBasedCompensationAwardTrancheThreeMember_C7719C55539034FE4E546042D97A6F4B" xlink:type="arc" />
    <link:label id="lab_mg_SharebasedCompensationAwardTrancheFourMember_E81F0294EB8A40C97A916042D97A26F2_terseLabel_en-US" xlink:label="lab_mg_SharebasedCompensationAwardTrancheFourMember_E81F0294EB8A40C97A916042D97A26F2" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">4th Anniversary</link:label>
    <link:label id="lab_mg_SharebasedCompensationAwardTrancheFourMember_E81F0294EB8A40C97A916042D97A26F2_label_en-US" xlink:label="lab_mg_SharebasedCompensationAwardTrancheFourMember_E81F0294EB8A40C97A916042D97A26F2" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Share-based Compensation Award, Tranche Four [Member]</link:label>
    <link:label id="lab_mg_SharebasedCompensationAwardTrancheFourMember_E81F0294EB8A40C97A916042D97A26F2_documentation_en-US" xlink:label="lab_mg_SharebasedCompensationAwardTrancheFourMember_E81F0294EB8A40C97A916042D97A26F2" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Share-based Compensation Award, Tranche Four</link:label>
    <link:loc xlink:href="mg-20181231.xsd#mg_SharebasedCompensationAwardTrancheFourMember" xlink:label="loc_mg_SharebasedCompensationAwardTrancheFourMember_E81F0294EB8A40C97A916042D97A26F2" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_mg_SharebasedCompensationAwardTrancheFourMember_E81F0294EB8A40C97A916042D97A26F2" xlink:to="lab_mg_SharebasedCompensationAwardTrancheFourMember_E81F0294EB8A40C97A916042D97A26F2" xlink:type="arc" />
    <link:label id="lab_us-gaap_BalanceSheetLocationAxis_9AFFFC6030BDAE98D0F76042D97A6C69_terseLabel_en-US" xlink:label="lab_us-gaap_BalanceSheetLocationAxis_9AFFFC6030BDAE98D0F76042D97A6C69" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Balance Sheet Location [Axis]</link:label>
    <link:label id="lab_us-gaap_BalanceSheetLocationAxis_9AFFFC6030BDAE98D0F76042D97A6C69_label_en-US" xlink:label="lab_us-gaap_BalanceSheetLocationAxis_9AFFFC6030BDAE98D0F76042D97A6C69" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Balance Sheet Location [Axis]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BalanceSheetLocationAxis" xlink:label="loc_us-gaap_BalanceSheetLocationAxis_9AFFFC6030BDAE98D0F76042D97A6C69" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_9AFFFC6030BDAE98D0F76042D97A6C69" xlink:to="lab_us-gaap_BalanceSheetLocationAxis_9AFFFC6030BDAE98D0F76042D97A6C69" xlink:type="arc" />
    <link:label id="lab_us-gaap_BalanceSheetLocationDomain_F6CC563EA3891B5A77B36042D97A3E00_terseLabel_en-US" xlink:label="lab_us-gaap_BalanceSheetLocationDomain_F6CC563EA3891B5A77B36042D97A3E00" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Balance Sheet Location [Domain]</link:label>
    <link:label id="lab_us-gaap_BalanceSheetLocationDomain_F6CC563EA3891B5A77B36042D97A3E00_label_en-US" xlink:label="lab_us-gaap_BalanceSheetLocationDomain_F6CC563EA3891B5A77B36042D97A3E00" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Balance Sheet Location [Domain]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BalanceSheetLocationDomain" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_F6CC563EA3891B5A77B36042D97A3E00" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_F6CC563EA3891B5A77B36042D97A3E00" xlink:to="lab_us-gaap_BalanceSheetLocationDomain_F6CC563EA3891B5A77B36042D97A3E00" xlink:type="arc" />
    <link:label id="lab_mg_AccruedExpensesandOtherCurrentLiabilitiesMember_02589D384FCD2681D6426042D9896D94_terseLabel_en-US" xlink:label="lab_mg_AccruedExpensesandOtherCurrentLiabilitiesMember_02589D384FCD2681D6426042D9896D94" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Accrued Expenses and Other Current Liabilities</link:label>
    <link:label id="lab_mg_AccruedExpensesandOtherCurrentLiabilitiesMember_02589D384FCD2681D6426042D9896D94_label_en-US" xlink:label="lab_mg_AccruedExpensesandOtherCurrentLiabilitiesMember_02589D384FCD2681D6426042D9896D94" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Accrued Expenses and Other Current Liabilities [Member]</link:label>
    <link:label id="lab_mg_AccruedExpensesandOtherCurrentLiabilitiesMember_02589D384FCD2681D6426042D9896D94_documentation_en-US" xlink:label="lab_mg_AccruedExpensesandOtherCurrentLiabilitiesMember_02589D384FCD2681D6426042D9896D94" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Accrued Expenses and Other Current Liabilities</link:label>
    <link:loc xlink:href="mg-20181231.xsd#mg_AccruedExpensesandOtherCurrentLiabilitiesMember" xlink:label="loc_mg_AccruedExpensesandOtherCurrentLiabilitiesMember_02589D384FCD2681D6426042D9896D94" xlink:type="locator" />
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    <link:label id="lab_mg_SharebasedCompensationArrangementbySharebasedPaymentAwardAwardPayoutPerformancePeriod_43C1EE44CB5A49D051CB6042D9898EC2_terseLabel_en-US" xlink:label="lab_mg_SharebasedCompensationArrangementbySharebasedPaymentAwardAwardPayoutPerformancePeriod_43C1EE44CB5A49D051CB6042D9898EC2" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Payout performance period</link:label>
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    <link:loc xlink:href="mg-20181231.xsd#mg_SharebasedCompensationArrangementbySharebasedPaymentAwardAwardPayoutPerformancePeriod" xlink:label="loc_mg_SharebasedCompensationArrangementbySharebasedPaymentAwardAwardPayoutPerformancePeriod_43C1EE44CB5A49D051CB6042D9898EC2" xlink:type="locator" />
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    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_0ADB8E866052FC1BAAC56042D9891901" xlink:type="locator" />
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    <link:label id="lab_us-gaap_NetCashProvidedByUsedInOperatingActivities_6D4F93863B217CD39215775D68F685D7_label_en-US" xlink:label="lab_us-gaap_NetCashProvidedByUsedInOperatingActivities_6D4F93863B217CD39215775D68F685D7" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Net Cash Provided by (Used in) Operating Activities</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_6D4F93863B217CD39215775D68F685D7" xlink:type="locator" />
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    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" xlink:label="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_7E379D92FB5A484699AD775D68F68798" xlink:type="locator" />
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    <link:label id="lab_mg_PaymentsToAcquireIntangibleAssetsAndSoftware_2C6F58D2159BC9F5622C775D68F63C66_negatedLabel_en-US" xlink:label="lab_mg_PaymentsToAcquireIntangibleAssetsAndSoftware_2C6F58D2159BC9F5622C775D68F63C66" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:type="resource" xml:lang="en-US">Purchase of intangible assets</link:label>
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    <link:label id="lab_mg_PaymentsToAcquireIntangibleAssetsAndSoftware_2C6F58D2159BC9F5622C775D68F63C66_documentation_en-US" xlink:label="lab_mg_PaymentsToAcquireIntangibleAssetsAndSoftware_2C6F58D2159BC9F5622C775D68F63C66" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">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.</link:label>
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    <link:label id="lab_us-gaap_ProceedsFromDivestitureOfBusinessesNetOfCashDivested_81640669EC12B0BC1D37775D68F7B6A2_terseLabel_en-US" xlink:label="lab_us-gaap_ProceedsFromDivestitureOfBusinessesNetOfCashDivested_81640669EC12B0BC1D37775D68F7B6A2" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Disposition of business</link:label>
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    <link:label id="lab_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_C7F71882DE694E3D4D11775D68F77927_label_en-US" xlink:label="lab_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_C7F71882DE694E3D4D11775D68F77927" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Payments to Acquire Businesses, Net of Cash Acquired</link:label>
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    <link:label id="lab_us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment_2D188FD113281933EF42775D68F7FEF3_terseLabel_en-US" xlink:label="lab_us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment_2D188FD113281933EF42775D68F7FEF3" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Proceeds from sale of equipment</link:label>
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    <link:label id="lab_us-gaap_NetCashProvidedByUsedInInvestingActivities_F885137B67F7025ABC24775D68F7940C_totalLabel_en-US" xlink:label="lab_us-gaap_NetCashProvidedByUsedInInvestingActivities_F885137B67F7025ABC24775D68F7940C" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xml:lang="en-US">Net cash used in investing activities</link:label>
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    <link:label id="lab_us-gaap_DebtInstrumentAxis_A293D1C7BC7BC11296295EA016E3F760_label_en-US" xlink:label="lab_us-gaap_DebtInstrumentAxis_A293D1C7BC7BC11296295EA016E3F760" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Debt Instrument [Axis]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentAxis" xlink:label="loc_us-gaap_DebtInstrumentAxis_A293D1C7BC7BC11296295EA016E3F760" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DebtInstrumentAxis_A293D1C7BC7BC11296295EA016E3F760" xlink:to="lab_us-gaap_DebtInstrumentAxis_A293D1C7BC7BC11296295EA016E3F760" xlink:type="arc" />
    <link:label id="lab_us-gaap_DebtInstrumentNameDomain_1D8FDD38E14AA1C5EFBC5EA016E30192_terseLabel_en-US" xlink:label="lab_us-gaap_DebtInstrumentNameDomain_1D8FDD38E14AA1C5EFBC5EA016E30192" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Debt Instrument, Name [Domain]</link:label>
    <link:label id="lab_us-gaap_DebtInstrumentNameDomain_1D8FDD38E14AA1C5EFBC5EA016E30192_label_en-US" xlink:label="lab_us-gaap_DebtInstrumentNameDomain_1D8FDD38E14AA1C5EFBC5EA016E30192" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Debt Instrument, Name [Domain]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_1D8FDD38E14AA1C5EFBC5EA016E30192" xlink:type="locator" />
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    <link:label id="lab_mg_TermALoanFacilityMember_7782CB21787AB191EB5A5EA016E3C515_terseLabel_en-US" xlink:label="lab_mg_TermALoanFacilityMember_7782CB21787AB191EB5A5EA016E3C515" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Term A Loan Facility</link:label>
    <link:label id="lab_mg_TermALoanFacilityMember_7782CB21787AB191EB5A5EA016E3C515_label_en-US" xlink:label="lab_mg_TermALoanFacilityMember_7782CB21787AB191EB5A5EA016E3C515" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Term A Loan Facility [Member]</link:label>
    <link:label id="lab_mg_TermALoanFacilityMember_7782CB21787AB191EB5A5EA016E3C515_documentation_en-US" xlink:label="lab_mg_TermALoanFacilityMember_7782CB21787AB191EB5A5EA016E3C515" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Term A Loan Facility</link:label>
    <link:loc xlink:href="mg-20181231.xsd#mg_TermALoanFacilityMember" xlink:label="loc_mg_TermALoanFacilityMember_7782CB21787AB191EB5A5EA016E3C515" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_mg_TermALoanFacilityMember_7782CB21787AB191EB5A5EA016E3C515" xlink:to="lab_mg_TermALoanFacilityMember_7782CB21787AB191EB5A5EA016E3C515" xlink:type="arc" />
    <link:label id="lab_us-gaap_VariableRateAxis_901B5F02428C2331BEEE5EA016E4BA6C_terseLabel_en-US" xlink:label="lab_us-gaap_VariableRateAxis_901B5F02428C2331BEEE5EA016E4BA6C" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Variable Rate [Axis]</link:label>
    <link:label id="lab_us-gaap_VariableRateAxis_901B5F02428C2331BEEE5EA016E4BA6C_label_en-US" xlink:label="lab_us-gaap_VariableRateAxis_901B5F02428C2331BEEE5EA016E4BA6C" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Variable Rate [Axis]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_VariableRateAxis" xlink:label="loc_us-gaap_VariableRateAxis_901B5F02428C2331BEEE5EA016E4BA6C" xlink:type="locator" />
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    <link:label id="lab_us-gaap_VariableRateDomain_62AF3CE7B64BBD401BAA5EA016E4C6FE_terseLabel_en-US" xlink:label="lab_us-gaap_VariableRateDomain_62AF3CE7B64BBD401BAA5EA016E4C6FE" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Variable Rate [Domain]</link:label>
    <link:label id="lab_us-gaap_VariableRateDomain_62AF3CE7B64BBD401BAA5EA016E4C6FE_label_en-US" xlink:label="lab_us-gaap_VariableRateDomain_62AF3CE7B64BBD401BAA5EA016E4C6FE" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Variable Rate [Domain]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_VariableRateDomain" xlink:label="loc_us-gaap_VariableRateDomain_62AF3CE7B64BBD401BAA5EA016E4C6FE" xlink:type="locator" />
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    <link:label id="lab_us-gaap_LondonInterbankOfferedRateLIBORMember_4C22586E82454E5658D35EA016E40C01_terseLabel_en-US" xlink:label="lab_us-gaap_LondonInterbankOfferedRateLIBORMember_4C22586E82454E5658D35EA016E40C01" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">LIBOR</link:label>
    <link:label id="lab_us-gaap_LondonInterbankOfferedRateLIBORMember_4C22586E82454E5658D35EA016E40C01_label_en-US" xlink:label="lab_us-gaap_LondonInterbankOfferedRateLIBORMember_4C22586E82454E5658D35EA016E40C01" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">London Interbank Offered Rate (LIBOR) [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LondonInterbankOfferedRateLIBORMember" xlink:label="loc_us-gaap_LondonInterbankOfferedRateLIBORMember_4C22586E82454E5658D35EA016E40C01" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LondonInterbankOfferedRateLIBORMember_4C22586E82454E5658D35EA016E40C01" xlink:to="lab_us-gaap_LondonInterbankOfferedRateLIBORMember_4C22586E82454E5658D35EA016E40C01" xlink:type="arc" />
    <link:label id="lab_us-gaap_BaseRateMember_7F4B9A9B65FA3B39BD105EA016E5C12B_terseLabel_en-US" xlink:label="lab_us-gaap_BaseRateMember_7F4B9A9B65FA3B39BD105EA016E5C12B" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Base rate</link:label>
    <link:label id="lab_us-gaap_BaseRateMember_7F4B9A9B65FA3B39BD105EA016E5C12B_label_en-US" xlink:label="lab_us-gaap_BaseRateMember_7F4B9A9B65FA3B39BD105EA016E5C12B" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Base Rate [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BaseRateMember" xlink:label="loc_us-gaap_BaseRateMember_7F4B9A9B65FA3B39BD105EA016E5C12B" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_BaseRateMember_7F4B9A9B65FA3B39BD105EA016E5C12B" xlink:to="lab_us-gaap_BaseRateMember_7F4B9A9B65FA3B39BD105EA016E5C12B" xlink:type="arc" />
    <link:label id="lab_us-gaap_DebtInstrumentLineItems_90D863B0EDB04E8173955EA016E6BD35_verboseLabel_en-US" xlink:label="lab_us-gaap_DebtInstrumentLineItems_90D863B0EDB04E8173955EA016E6BD35" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:type="resource" xml:lang="en-US">Long-Term Debt</link:label>
    <link:label id="lab_us-gaap_DebtInstrumentLineItems_90D863B0EDB04E8173955EA016E6BD35_label_en-US" xlink:label="lab_us-gaap_DebtInstrumentLineItems_90D863B0EDB04E8173955EA016E6BD35" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Debt Instrument [Line Items]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentLineItems" xlink:label="loc_us-gaap_DebtInstrumentLineItems_90D863B0EDB04E8173955EA016E6BD35" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DebtInstrumentLineItems_90D863B0EDB04E8173955EA016E6BD35" xlink:to="lab_us-gaap_DebtInstrumentLineItems_90D863B0EDB04E8173955EA016E6BD35" xlink:type="arc" />
    <link:label id="lab_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_9AC4ECDC5C2E1A13B1BD5EA016E6429A_terseLabel_en-US" xlink:label="lab_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_9AC4ECDC5C2E1A13B1BD5EA016E6429A" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Maximum borrowing capacity</link:label>
    <link:label id="lab_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_9AC4ECDC5C2E1A13B1BD5EA016E6429A_label_en-US" xlink:label="lab_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_9AC4ECDC5C2E1A13B1BD5EA016E6429A" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Line of Credit Facility, Maximum Borrowing Capacity</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_9AC4ECDC5C2E1A13B1BD5EA016E6429A" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_9AC4ECDC5C2E1A13B1BD5EA016E6429A" xlink:to="lab_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_9AC4ECDC5C2E1A13B1BD5EA016E6429A" xlink:type="arc" />
    <link:label id="lab_mg_LineOfCreditFacilityAccordionFeatureHigherBorrowingCapacityOption_A00B47253B3BEBBB52665EA016E7C05F_terseLabel_en-US" xlink:label="lab_mg_LineOfCreditFacilityAccordionFeatureHigherBorrowingCapacityOption_A00B47253B3BEBBB52665EA016E7C05F" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Higher borrowing capacity option</link:label>
    <link:label id="lab_mg_LineOfCreditFacilityAccordionFeatureHigherBorrowingCapacityOption_A00B47253B3BEBBB52665EA016E7C05F_label_en-US" xlink:label="lab_mg_LineOfCreditFacilityAccordionFeatureHigherBorrowingCapacityOption_A00B47253B3BEBBB52665EA016E7C05F" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Line Of Credit Facility, Accordion Feature, Higher Borrowing Capacity Option</link:label>
    <link:label id="lab_mg_LineOfCreditFacilityAccordionFeatureHigherBorrowingCapacityOption_A00B47253B3BEBBB52665EA016E7C05F_documentation_en-US" xlink:label="lab_mg_LineOfCreditFacilityAccordionFeatureHigherBorrowingCapacityOption_A00B47253B3BEBBB52665EA016E7C05F" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Line Of Credit Facility, Accordion Feature, Higher Borrowing Capacity Option</link:label>
    <link:loc xlink:href="mg-20181231.xsd#mg_LineOfCreditFacilityAccordionFeatureHigherBorrowingCapacityOption" xlink:label="loc_mg_LineOfCreditFacilityAccordionFeatureHigherBorrowingCapacityOption_A00B47253B3BEBBB52665EA016E7C05F" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_mg_LineOfCreditFacilityAccordionFeatureHigherBorrowingCapacityOption_A00B47253B3BEBBB52665EA016E7C05F" xlink:to="lab_mg_LineOfCreditFacilityAccordionFeatureHigherBorrowingCapacityOption_A00B47253B3BEBBB52665EA016E7C05F" xlink:type="arc" />
    <link:label id="lab_mg_LineOfCreditFacilityMaximumBorrowingCapacityInNonUSCurrencies_E391635F44C51794732E5EA016E7FB12_terseLabel_en-US" xlink:label="lab_mg_LineOfCreditFacilityMaximumBorrowingCapacityInNonUSCurrencies_E391635F44C51794732E5EA016E7FB12" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Maximum borrowing capacity in non-U.S. Dollar currencies</link:label>
    <link:label id="lab_mg_LineOfCreditFacilityMaximumBorrowingCapacityInNonUSCurrencies_E391635F44C51794732E5EA016E7FB12_label_en-US" xlink:label="lab_mg_LineOfCreditFacilityMaximumBorrowingCapacityInNonUSCurrencies_E391635F44C51794732E5EA016E7FB12" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Line of Credit Facility Maximum Borrowing Capacity in Non US Currencies</link:label>
    <link:label id="lab_mg_LineOfCreditFacilityMaximumBorrowingCapacityInNonUSCurrencies_E391635F44C51794732E5EA016E7FB12_documentation_en-US" xlink:label="lab_mg_LineOfCreditFacilityMaximumBorrowingCapacityInNonUSCurrencies_E391635F44C51794732E5EA016E7FB12" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Represents the maximum borrowing capacity in non-U.S. dollar currencies under the revolving credit facility.</link:label>
    <link:loc xlink:href="mg-20181231.xsd#mg_LineOfCreditFacilityMaximumBorrowingCapacityInNonUSCurrencies" xlink:label="loc_mg_LineOfCreditFacilityMaximumBorrowingCapacityInNonUSCurrencies_E391635F44C51794732E5EA016E7FB12" xlink:type="locator" />
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    <link:label id="lab_mg_LineOfCreditFacilityMaximumBorrowingCapacityAvailableForIssuanceOfLettersOfCredit_5CF0A427FBBBD399F2095EA016E71ED4_terseLabel_en-US" xlink:label="lab_mg_LineOfCreditFacilityMaximumBorrowingCapacityAvailableForIssuanceOfLettersOfCredit_5CF0A427FBBBD399F2095EA016E71ED4" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Maximum amount available for the issuance of letters of credit</link:label>
    <link:label id="lab_mg_LineOfCreditFacilityMaximumBorrowingCapacityAvailableForIssuanceOfLettersOfCredit_5CF0A427FBBBD399F2095EA016E71ED4_label_en-US" xlink:label="lab_mg_LineOfCreditFacilityMaximumBorrowingCapacityAvailableForIssuanceOfLettersOfCredit_5CF0A427FBBBD399F2095EA016E71ED4" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Line of Credit Facility Maximum Borrowing Capacity Available for Issuance of Letters of Credit</link:label>
    <link:label id="lab_mg_LineOfCreditFacilityMaximumBorrowingCapacityAvailableForIssuanceOfLettersOfCredit_5CF0A427FBBBD399F2095EA016E71ED4_documentation_en-US" xlink:label="lab_mg_LineOfCreditFacilityMaximumBorrowingCapacityAvailableForIssuanceOfLettersOfCredit_5CF0A427FBBBD399F2095EA016E71ED4" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Represents the maximum amount of borrowing capacity under the revolving credit facility that is available for the issuance of letters of credit.</link:label>
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    <link:label id="lab_mg_LongtermDebtExcludingLettersofCredit_F2581664D6A0F1E0550A5EA01B5972E4_terseLabel_en-US" xlink:label="lab_mg_LongtermDebtExcludingLettersofCredit_F2581664D6A0F1E0550A5EA01B5972E4" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Total borrowings outstanding</link:label>
    <link:label id="lab_mg_LongtermDebtExcludingLettersofCredit_F2581664D6A0F1E0550A5EA01B5972E4_label_en-US" xlink:label="lab_mg_LongtermDebtExcludingLettersofCredit_F2581664D6A0F1E0550A5EA01B5972E4" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Long-term Debt, Excluding Letters of Credit</link:label>
    <link:label id="lab_mg_LongtermDebtExcludingLettersofCredit_F2581664D6A0F1E0550A5EA01B5972E4_documentation_en-US" xlink:label="lab_mg_LongtermDebtExcludingLettersofCredit_F2581664D6A0F1E0550A5EA01B5972E4" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Long-term Debt, Excluding Letters of Credit</link:label>
    <link:loc xlink:href="mg-20181231.xsd#mg_LongtermDebtExcludingLettersofCredit" xlink:label="loc_mg_LongtermDebtExcludingLettersofCredit_F2581664D6A0F1E0550A5EA01B5972E4" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_mg_LongtermDebtExcludingLettersofCredit_F2581664D6A0F1E0550A5EA01B5972E4" xlink:to="lab_mg_LongtermDebtExcludingLettersofCredit_F2581664D6A0F1E0550A5EA01B5972E4" xlink:type="arc" />
    <link:label id="lab_us-gaap_LettersOfCreditOutstandingAmount_CBE3DB85D62CC37AFF915EA016E75212_terseLabel_en-US" xlink:label="lab_us-gaap_LettersOfCreditOutstandingAmount_CBE3DB85D62CC37AFF915EA016E75212" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Outstanding letters of credit</link:label>
    <link:label id="lab_us-gaap_LettersOfCreditOutstandingAmount_CBE3DB85D62CC37AFF915EA016E75212_label_en-US" xlink:label="lab_us-gaap_LettersOfCreditOutstandingAmount_CBE3DB85D62CC37AFF915EA016E75212" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Letters of Credit Outstanding, Amount</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LettersOfCreditOutstandingAmount" xlink:label="loc_us-gaap_LettersOfCreditOutstandingAmount_CBE3DB85D62CC37AFF915EA016E75212" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LettersOfCreditOutstandingAmount_CBE3DB85D62CC37AFF915EA016E75212" xlink:to="lab_us-gaap_LettersOfCreditOutstandingAmount_CBE3DB85D62CC37AFF915EA016E75212" xlink:type="arc" />
    <link:label id="lab_us-gaap_UnamortizedDebtIssuanceExpense_DCC5524D972D468E7C8D5EA016E7D54B_terseLabel_en-US" xlink:label="lab_us-gaap_UnamortizedDebtIssuanceExpense_DCC5524D972D468E7C8D5EA016E7D54B" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Capitalized debt modification costs</link:label>
    <link:label id="lab_us-gaap_UnamortizedDebtIssuanceExpense_DCC5524D972D468E7C8D5EA016E7D54B_label_en-US" xlink:label="lab_us-gaap_UnamortizedDebtIssuanceExpense_DCC5524D972D468E7C8D5EA016E7D54B" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Unamortized Debt Issuance Expense</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_UnamortizedDebtIssuanceExpense" xlink:label="loc_us-gaap_UnamortizedDebtIssuanceExpense_DCC5524D972D468E7C8D5EA016E7D54B" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_UnamortizedDebtIssuanceExpense_DCC5524D972D468E7C8D5EA016E7D54B" xlink:to="lab_us-gaap_UnamortizedDebtIssuanceExpense_DCC5524D972D468E7C8D5EA016E7D54B" xlink:type="arc" />
    <link:label id="lab_us-gaap_DebtInstrumentDescriptionOfVariableRateBasis_9F9AB931FEA6DC0092D85EA016E8186A_terseLabel_en-US" xlink:label="lab_us-gaap_DebtInstrumentDescriptionOfVariableRateBasis_9F9AB931FEA6DC0092D85EA016E8186A" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Reference rate, description</link:label>
    <link:label id="lab_us-gaap_DebtInstrumentDescriptionOfVariableRateBasis_9F9AB931FEA6DC0092D85EA016E8186A_label_en-US" xlink:label="lab_us-gaap_DebtInstrumentDescriptionOfVariableRateBasis_9F9AB931FEA6DC0092D85EA016E8186A" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Debt Instrument, Description of Variable Rate Basis</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentDescriptionOfVariableRateBasis" xlink:label="loc_us-gaap_DebtInstrumentDescriptionOfVariableRateBasis_9F9AB931FEA6DC0092D85EA016E8186A" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DebtInstrumentDescriptionOfVariableRateBasis_9F9AB931FEA6DC0092D85EA016E8186A" xlink:to="lab_us-gaap_DebtInstrumentDescriptionOfVariableRateBasis_9F9AB931FEA6DC0092D85EA016E8186A" xlink:type="arc" />
    <link:label id="lab_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_97E77322114054B467155EA016E87B4D_terseLabel_en-US" xlink:label="lab_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_97E77322114054B467155EA016E87B4D" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Margin rate (as a percent)</link:label>
    <link:label id="lab_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_97E77322114054B467155EA016E87B4D_label_en-US" xlink:label="lab_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_97E77322114054B467155EA016E87B4D" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Debt Instrument, Basis Spread on Variable Rate</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_97E77322114054B467155EA016E87B4D" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_97E77322114054B467155EA016E87B4D" xlink:to="lab_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_97E77322114054B467155EA016E87B4D" xlink:type="arc" />
    <link:label id="lab_mg_DebtInstrumentNonrecurringChargesThresholdUsedForCalculationofFundedDebtLeverageRatio_B4A1885F4B9B5FAB93375EA016E8A52B_terseLabel_en-US" xlink:label="lab_mg_DebtInstrumentNonrecurringChargesThresholdUsedForCalculationofFundedDebtLeverageRatio_B4A1885F4B9B5FAB93375EA016E8A52B" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Non-recurring charges threshold used for calculation of funded debt leverage ratio</link:label>
    <link:label id="lab_mg_DebtInstrumentNonrecurringChargesThresholdUsedForCalculationofFundedDebtLeverageRatio_B4A1885F4B9B5FAB93375EA016E8A52B_label_en-US" xlink:label="lab_mg_DebtInstrumentNonrecurringChargesThresholdUsedForCalculationofFundedDebtLeverageRatio_B4A1885F4B9B5FAB93375EA016E8A52B" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Debt Instrument, Non-recurring Charges Threshold Used For Calculation of Funded Debt Leverage Ratio</link:label>
    <link:label id="lab_mg_DebtInstrumentNonrecurringChargesThresholdUsedForCalculationofFundedDebtLeverageRatio_B4A1885F4B9B5FAB93375EA016E8A52B_documentation_en-US" xlink:label="lab_mg_DebtInstrumentNonrecurringChargesThresholdUsedForCalculationofFundedDebtLeverageRatio_B4A1885F4B9B5FAB93375EA016E8A52B" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Debt Instrument, Non-recurring Charges Threshold Used For Calculation of Funded Debt Leverage Ratio</link:label>
    <link:loc xlink:href="mg-20181231.xsd#mg_DebtInstrumentNonrecurringChargesThresholdUsedForCalculationofFundedDebtLeverageRatio" xlink:label="loc_mg_DebtInstrumentNonrecurringChargesThresholdUsedForCalculationofFundedDebtLeverageRatio_B4A1885F4B9B5FAB93375EA016E8A52B" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_mg_DebtInstrumentNonrecurringChargesThresholdUsedForCalculationofFundedDebtLeverageRatio_B4A1885F4B9B5FAB93375EA016E8A52B" xlink:to="lab_mg_DebtInstrumentNonrecurringChargesThresholdUsedForCalculationofFundedDebtLeverageRatio_B4A1885F4B9B5FAB93375EA016E8A52B" xlink:type="arc" />
    <link:label id="lab_mg_DebtInstrumentNumberOfFiscalQuartersUsedForCalculationOfFundedDebtLeverageRatio_D5795A7C315359ABC79B5EA016E86044_terseLabel_en-US" xlink:label="lab_mg_DebtInstrumentNumberOfFiscalQuartersUsedForCalculationOfFundedDebtLeverageRatio_D5795A7C315359ABC79B5EA016E86044" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Number of consecutive fiscal quarters used for calculating funded debt leverage ratio</link:label>
    <link:label id="lab_mg_DebtInstrumentNumberOfFiscalQuartersUsedForCalculationOfFundedDebtLeverageRatio_D5795A7C315359ABC79B5EA016E86044_label_en-US" xlink:label="lab_mg_DebtInstrumentNumberOfFiscalQuartersUsedForCalculationOfFundedDebtLeverageRatio_D5795A7C315359ABC79B5EA016E86044" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Debt Instrument, Number of Fiscal Quarters Used for Calculation of Funded Debt Leverage Ratio</link:label>
    <link:label id="lab_mg_DebtInstrumentNumberOfFiscalQuartersUsedForCalculationOfFundedDebtLeverageRatio_D5795A7C315359ABC79B5EA016E86044_documentation_en-US" xlink:label="lab_mg_DebtInstrumentNumberOfFiscalQuartersUsedForCalculationOfFundedDebtLeverageRatio_D5795A7C315359ABC79B5EA016E86044" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Represents the number of consecutive fiscal quarters immediately preceding the date of determination of the Funded Debt Leverage Ratio.</link:label>
    <link:loc xlink:href="mg-20181231.xsd#mg_DebtInstrumentNumberOfFiscalQuartersUsedForCalculationOfFundedDebtLeverageRatio" xlink:label="loc_mg_DebtInstrumentNumberOfFiscalQuartersUsedForCalculationOfFundedDebtLeverageRatio_D5795A7C315359ABC79B5EA016E86044" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_mg_DebtInstrumentNumberOfFiscalQuartersUsedForCalculationOfFundedDebtLeverageRatio_D5795A7C315359ABC79B5EA016E86044" xlink:to="lab_mg_DebtInstrumentNumberOfFiscalQuartersUsedForCalculationOfFundedDebtLeverageRatio_D5795A7C315359ABC79B5EA016E86044" xlink:type="arc" />
    <link:label id="lab_mg_DebtInstrumentCovenantFundedLeverageRatioConsideredForLowerInterestRateMargin_1C4D695FCBE9D56A0A8F5EA016E8314E_terseLabel_en-US" xlink:label="lab_mg_DebtInstrumentCovenantFundedLeverageRatioConsideredForLowerInterestRateMargin_1C4D695FCBE9D56A0A8F5EA016E8314E" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Funded debt leverage ratio at which the entity will have the benefit of lowest interest margin</link:label>
    <link:label id="lab_mg_DebtInstrumentCovenantFundedLeverageRatioConsideredForLowerInterestRateMargin_1C4D695FCBE9D56A0A8F5EA016E8314E_label_en-US" xlink:label="lab_mg_DebtInstrumentCovenantFundedLeverageRatioConsideredForLowerInterestRateMargin_1C4D695FCBE9D56A0A8F5EA016E8314E" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Debt Instrument, Covenant Funded Leverage Ratio Considered for Lower Interest Rate Margin</link:label>
    <link:label id="lab_mg_DebtInstrumentCovenantFundedLeverageRatioConsideredForLowerInterestRateMargin_1C4D695FCBE9D56A0A8F5EA016E8314E_documentation_en-US" xlink:label="lab_mg_DebtInstrumentCovenantFundedLeverageRatioConsideredForLowerInterestRateMargin_1C4D695FCBE9D56A0A8F5EA016E8314E" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Represents the Funded Debt Leverage Ratio at which the entity will have the benefit of lower interest rate margin.</link:label>
    <link:loc xlink:href="mg-20181231.xsd#mg_DebtInstrumentCovenantFundedLeverageRatioConsideredForLowerInterestRateMargin" xlink:label="loc_mg_DebtInstrumentCovenantFundedLeverageRatioConsideredForLowerInterestRateMargin_1C4D695FCBE9D56A0A8F5EA016E8314E" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_mg_DebtInstrumentCovenantFundedLeverageRatioConsideredForLowerInterestRateMargin_1C4D695FCBE9D56A0A8F5EA016E8314E" xlink:to="lab_mg_DebtInstrumentCovenantFundedLeverageRatioConsideredForLowerInterestRateMargin_1C4D695FCBE9D56A0A8F5EA016E8314E" xlink:type="arc" />
    <link:label id="lab_mg_DebtInstrumentCovenantFundedLeverageRatioConsideredForMaximumInterestRateMargin_DBB6432E63C7D9D787665EA016E80377_terseLabel_en-US" xlink:label="lab_mg_DebtInstrumentCovenantFundedLeverageRatioConsideredForMaximumInterestRateMargin_DBB6432E63C7D9D787665EA016E80377" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Funded debt leverage ratio at which the entity will bear the maximum interest rate margin</link:label>
    <link:label id="lab_mg_DebtInstrumentCovenantFundedLeverageRatioConsideredForMaximumInterestRateMargin_DBB6432E63C7D9D787665EA016E80377_label_en-US" xlink:label="lab_mg_DebtInstrumentCovenantFundedLeverageRatioConsideredForMaximumInterestRateMargin_DBB6432E63C7D9D787665EA016E80377" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Debt Instrument, Covenant Funded Leverage Ratio Considered for Maximum Interest Rate Margin</link:label>
    <link:label id="lab_mg_DebtInstrumentCovenantFundedLeverageRatioConsideredForMaximumInterestRateMargin_DBB6432E63C7D9D787665EA016E80377_documentation_en-US" xlink:label="lab_mg_DebtInstrumentCovenantFundedLeverageRatioConsideredForMaximumInterestRateMargin_DBB6432E63C7D9D787665EA016E80377" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Represents the Funded Debt Leverage Ratio at which the entity will have the maximum interest rate margin.</link:label>
    <link:loc xlink:href="mg-20181231.xsd#mg_DebtInstrumentCovenantFundedLeverageRatioConsideredForMaximumInterestRateMargin" xlink:label="loc_mg_DebtInstrumentCovenantFundedLeverageRatioConsideredForMaximumInterestRateMargin_DBB6432E63C7D9D787665EA016E80377" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_mg_DebtInstrumentCovenantFundedLeverageRatioConsideredForMaximumInterestRateMargin_DBB6432E63C7D9D787665EA016E80377" xlink:to="lab_mg_DebtInstrumentCovenantFundedLeverageRatioConsideredForMaximumInterestRateMargin_DBB6432E63C7D9D787665EA016E80377" xlink:type="arc" />
    <link:label id="lab_mg_DebtInstrumentAdditionalInterestRateDueToFundedDebtLeverageRatioExceedingSpecifiedThreshold_CD169726E3C34530A49B5EA016E989CE_terseLabel_en-US" xlink:label="lab_mg_DebtInstrumentAdditionalInterestRateDueToFundedDebtLeverageRatioExceedingSpecifiedThreshold_CD169726E3C34530A49B5EA016E989CE" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Additional interest rate margin if funded debt leverage ratio exceeds threshold (as a percent)</link:label>
    <link:label id="lab_mg_DebtInstrumentAdditionalInterestRateDueToFundedDebtLeverageRatioExceedingSpecifiedThreshold_CD169726E3C34530A49B5EA016E989CE_label_en-US" xlink:label="lab_mg_DebtInstrumentAdditionalInterestRateDueToFundedDebtLeverageRatioExceedingSpecifiedThreshold_CD169726E3C34530A49B5EA016E989CE" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Debt Instrument, Additional Interest Rate Due to Funded Debt Leverage Ratio Exceeding Specified Threshold</link:label>
    <link:label id="lab_mg_DebtInstrumentAdditionalInterestRateDueToFundedDebtLeverageRatioExceedingSpecifiedThreshold_CD169726E3C34530A49B5EA016E989CE_documentation_en-US" xlink:label="lab_mg_DebtInstrumentAdditionalInterestRateDueToFundedDebtLeverageRatioExceedingSpecifiedThreshold_CD169726E3C34530A49B5EA016E989CE" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">The percentage points added to the reference rate due to the Funded Debt Leverage Ratio, which is used to compute the variable rate on the debt instrument, exceeding a specified threshold.</link:label>
    <link:loc xlink:href="mg-20181231.xsd#mg_DebtInstrumentAdditionalInterestRateDueToFundedDebtLeverageRatioExceedingSpecifiedThreshold" xlink:label="loc_mg_DebtInstrumentAdditionalInterestRateDueToFundedDebtLeverageRatioExceedingSpecifiedThreshold_CD169726E3C34530A49B5EA016E989CE" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_mg_DebtInstrumentAdditionalInterestRateDueToFundedDebtLeverageRatioExceedingSpecifiedThreshold_CD169726E3C34530A49B5EA016E989CE" xlink:to="lab_mg_DebtInstrumentAdditionalInterestRateDueToFundedDebtLeverageRatioExceedingSpecifiedThreshold_CD169726E3C34530A49B5EA016E989CE" xlink:type="arc" />
    <link:label id="lab_mg_DebtInstrumentCovenantFundedDebtLeverageRatioForAdditionalInterestPayment_D93BA0FEC988173DF33C5EA016E904DA_terseLabel_en-US" xlink:label="lab_mg_DebtInstrumentCovenantFundedDebtLeverageRatioForAdditionalInterestPayment_D93BA0FEC988173DF33C5EA016E904DA" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Funded debt leverage ratio for additional interest payment</link:label>
    <link:label id="lab_mg_DebtInstrumentCovenantFundedDebtLeverageRatioForAdditionalInterestPayment_D93BA0FEC988173DF33C5EA016E904DA_label_en-US" xlink:label="lab_mg_DebtInstrumentCovenantFundedDebtLeverageRatioForAdditionalInterestPayment_D93BA0FEC988173DF33C5EA016E904DA" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Debt Instrument, Covenant Funded Debt Leverage Ratio for Additional Interest Payment</link:label>
    <link:label id="lab_mg_DebtInstrumentCovenantFundedDebtLeverageRatioForAdditionalInterestPayment_D93BA0FEC988173DF33C5EA016E904DA_documentation_en-US" xlink:label="lab_mg_DebtInstrumentCovenantFundedDebtLeverageRatioForAdditionalInterestPayment_D93BA0FEC988173DF33C5EA016E904DA" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Represents the Funded Debt Leverage Ratio on which the entity will bear an additional interest on debt.</link:label>
    <link:loc xlink:href="mg-20181231.xsd#mg_DebtInstrumentCovenantFundedDebtLeverageRatioForAdditionalInterestPayment" xlink:label="loc_mg_DebtInstrumentCovenantFundedDebtLeverageRatioForAdditionalInterestPayment_D93BA0FEC988173DF33C5EA016E904DA" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_mg_DebtInstrumentCovenantFundedDebtLeverageRatioForAdditionalInterestPayment_D93BA0FEC988173DF33C5EA016E904DA" xlink:to="lab_mg_DebtInstrumentCovenantFundedDebtLeverageRatioForAdditionalInterestPayment_D93BA0FEC988173DF33C5EA016E904DA" xlink:type="arc" />
    <link:label id="lab_mg_DebtInstrumentCovenantInterestCoverageRatio_B4EC847E8109F258CB065EA016E959BE_terseLabel_en-US" xlink:label="lab_mg_DebtInstrumentCovenantInterestCoverageRatio_B4EC847E8109F258CB065EA016E959BE" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Interest coverage ratio</link:label>
    <link:label id="lab_mg_DebtInstrumentCovenantInterestCoverageRatio_B4EC847E8109F258CB065EA016E959BE_label_en-US" xlink:label="lab_mg_DebtInstrumentCovenantInterestCoverageRatio_B4EC847E8109F258CB065EA016E959BE" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Debt Instrument, Covenant Interest Coverage Ratio</link:label>
    <link:label id="lab_mg_DebtInstrumentCovenantInterestCoverageRatio_B4EC847E8109F258CB065EA016E959BE_documentation_en-US" xlink:label="lab_mg_DebtInstrumentCovenantInterestCoverageRatio_B4EC847E8109F258CB065EA016E959BE" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Represents the Interest Coverage Ratio required under the terms of the covenants.</link:label>
    <link:loc xlink:href="mg-20181231.xsd#mg_DebtInstrumentCovenantInterestCoverageRatio" xlink:label="loc_mg_DebtInstrumentCovenantInterestCoverageRatio_B4EC847E8109F258CB065EA016E959BE" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_mg_DebtInstrumentCovenantInterestCoverageRatio_B4EC847E8109F258CB065EA016E959BE" xlink:to="lab_mg_DebtInstrumentCovenantInterestCoverageRatio_B4EC847E8109F258CB065EA016E959BE" xlink:type="arc" />
    <link:label id="lab_mg_DebtInstrumentPrecedingPeriodUsedForCalculationOfInterestCoverageRatio_F81F5AA1BDB34692F1BC5EA016E9CB24_terseLabel_en-US" xlink:label="lab_mg_DebtInstrumentPrecedingPeriodUsedForCalculationOfInterestCoverageRatio_F81F5AA1BDB34692F1BC5EA016E9CB24" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Preceding period used for calculating interest coverage ratio</link:label>
    <link:label id="lab_mg_DebtInstrumentPrecedingPeriodUsedForCalculationOfInterestCoverageRatio_F81F5AA1BDB34692F1BC5EA016E9CB24_label_en-US" xlink:label="lab_mg_DebtInstrumentPrecedingPeriodUsedForCalculationOfInterestCoverageRatio_F81F5AA1BDB34692F1BC5EA016E9CB24" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Debt Instrument, Preceding Period Used for Calculation of Interest Coverage Ratio</link:label>
    <link:label id="lab_mg_DebtInstrumentPrecedingPeriodUsedForCalculationOfInterestCoverageRatio_F81F5AA1BDB34692F1BC5EA016E9CB24_documentation_en-US" xlink:label="lab_mg_DebtInstrumentPrecedingPeriodUsedForCalculationOfInterestCoverageRatio_F81F5AA1BDB34692F1BC5EA016E9CB24" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Represents the preceding period used for determination of the Interest Coverage Ratio.</link:label>
    <link:loc xlink:href="mg-20181231.xsd#mg_DebtInstrumentPrecedingPeriodUsedForCalculationOfInterestCoverageRatio" xlink:label="loc_mg_DebtInstrumentPrecedingPeriodUsedForCalculationOfInterestCoverageRatio_F81F5AA1BDB34692F1BC5EA016E9CB24" xlink:type="locator" />
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    <link:label id="lab_mg_DebtInstrumentCovenantTemporarilyIncreaseinFundedDebtLeverageRatioduetoBusinessAcquisitions_A46104556B208F6D10C45EA016E94D59_terseLabel_en-US" xlink:label="lab_mg_DebtInstrumentCovenantTemporarilyIncreaseinFundedDebtLeverageRatioduetoBusinessAcquisitions_A46104556B208F6D10C45EA016E94D59" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Funded debt leverage ratio temporarily increase due to business acquisitions</link:label>
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    <link:label id="lab_us-gaap_ScheduleOfFutureMinimumRentalPaymentsForOperatingLeasesTableTextBlock_D681E553F34545D7860C3470525BE7ED_terseLabel_en-US" xlink:label="lab_us-gaap_ScheduleOfFutureMinimumRentalPaymentsForOperatingLeasesTableTextBlock_D681E553F34545D7860C3470525BE7ED" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Schedule of Future Minimum Lease Payments Under Noncancelable Operating Leases</link:label>
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    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfFutureMinimumRentalPaymentsForOperatingLeasesTableTextBlock" xlink:label="loc_us-gaap_ScheduleOfFutureMinimumRentalPaymentsForOperatingLeasesTableTextBlock_D681E553F34545D7860C3470525BE7ED" xlink:type="locator" />
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    <link:label id="lab_us-gaap_PlanNameAxis_60E1F9A4CCF57121ED568185174EDF0B_terseLabel_en-US" xlink:label="lab_us-gaap_PlanNameAxis_60E1F9A4CCF57121ED568185174EDF0B" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Plan Name [Axis]</link:label>
    <link:label id="lab_us-gaap_PlanNameAxis_60E1F9A4CCF57121ED568185174EDF0B_label_en-US" xlink:label="lab_us-gaap_PlanNameAxis_60E1F9A4CCF57121ED568185174EDF0B" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Plan Name [Axis]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PlanNameAxis" xlink:label="loc_us-gaap_PlanNameAxis_60E1F9A4CCF57121ED568185174EDF0B" xlink:type="locator" />
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    <link:label id="lab_us-gaap_PlanNameDomain_4C4B098B68A08D0723FB8185174E45F2_terseLabel_en-US" xlink:label="lab_us-gaap_PlanNameDomain_4C4B098B68A08D0723FB8185174E45F2" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Plan Name [Domain]</link:label>
    <link:label id="lab_us-gaap_PlanNameDomain_4C4B098B68A08D0723FB8185174E45F2_label_en-US" xlink:label="lab_us-gaap_PlanNameDomain_4C4B098B68A08D0723FB8185174E45F2" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Plan Name [Domain]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaap_PlanNameDomain_4C4B098B68A08D0723FB8185174E45F2" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_PlanNameDomain_4C4B098B68A08D0723FB8185174E45F2" xlink:to="lab_us-gaap_PlanNameDomain_4C4B098B68A08D0723FB8185174E45F2" xlink:type="arc" />
    <link:label id="lab_mg_StockOptionPlan2007andLongTermIncentivePlan2009Member_0C1BB85A7ECF6C998B6F8185174FBE00_terseLabel_en-US" xlink:label="lab_mg_StockOptionPlan2007andLongTermIncentivePlan2009Member_0C1BB85A7ECF6C998B6F8185174FBE00" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">2007 Plan and 2009 Plan</link:label>
    <link:label id="lab_mg_StockOptionPlan2007andLongTermIncentivePlan2009Member_0C1BB85A7ECF6C998B6F8185174FBE00_label_en-US" xlink:label="lab_mg_StockOptionPlan2007andLongTermIncentivePlan2009Member_0C1BB85A7ECF6C998B6F8185174FBE00" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Stock Option Plan 2007 and Long Term Incentive Plan 2009 [Member]</link:label>
    <link:label id="lab_mg_StockOptionPlan2007andLongTermIncentivePlan2009Member_0C1BB85A7ECF6C998B6F8185174FBE00_documentation_en-US" xlink:label="lab_mg_StockOptionPlan2007andLongTermIncentivePlan2009Member_0C1BB85A7ECF6C998B6F8185174FBE00" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Stock Option Plan 2007 and Long Term Incentive Plan 2009</link:label>
    <link:loc xlink:href="mg-20181231.xsd#mg_StockOptionPlan2007andLongTermIncentivePlan2009Member" xlink:label="loc_mg_StockOptionPlan2007andLongTermIncentivePlan2009Member_0C1BB85A7ECF6C998B6F8185174FBE00" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_mg_StockOptionPlan2007andLongTermIncentivePlan2009Member_0C1BB85A7ECF6C998B6F8185174FBE00" xlink:to="lab_mg_StockOptionPlan2007andLongTermIncentivePlan2009Member_0C1BB85A7ECF6C998B6F8185174FBE00" xlink:type="arc" />
    <link:label id="lab_mg_LongTermIncentivePlan2016Member_5D97CB6A5C33BD1217398185174F57C2_terseLabel_en-US" xlink:label="lab_mg_LongTermIncentivePlan2016Member_5D97CB6A5C33BD1217398185174F57C2" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">2016 Plan</link:label>
    <link:label id="lab_mg_LongTermIncentivePlan2016Member_5D97CB6A5C33BD1217398185174F57C2_label_en-US" xlink:label="lab_mg_LongTermIncentivePlan2016Member_5D97CB6A5C33BD1217398185174F57C2" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Long Term Incentive Plan 2016 [Member]</link:label>
    <link:label id="lab_mg_LongTermIncentivePlan2016Member_5D97CB6A5C33BD1217398185174F57C2_documentation_en-US" xlink:label="lab_mg_LongTermIncentivePlan2016Member_5D97CB6A5C33BD1217398185174F57C2" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Long Term Incentive Plan 2016</link:label>
    <link:loc xlink:href="mg-20181231.xsd#mg_LongTermIncentivePlan2016Member" xlink:label="loc_mg_LongTermIncentivePlan2016Member_5D97CB6A5C33BD1217398185174F57C2" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_mg_LongTermIncentivePlan2016Member_5D97CB6A5C33BD1217398185174F57C2" xlink:to="lab_mg_LongTermIncentivePlan2016Member_5D97CB6A5C33BD1217398185174F57C2" xlink:type="arc" />
    <link:label id="lab_mg_EmployeeStockOwnershipPlanNumberOfPlans_71349FF1AB3BDE705B0B81851750C59B_terseLabel_en-US" xlink:label="lab_mg_EmployeeStockOwnershipPlanNumberOfPlans_71349FF1AB3BDE705B0B81851750C59B" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Number of employee stock ownership plans</link:label>
    <link:label id="lab_mg_EmployeeStockOwnershipPlanNumberOfPlans_71349FF1AB3BDE705B0B81851750C59B_label_en-US" xlink:label="lab_mg_EmployeeStockOwnershipPlanNumberOfPlans_71349FF1AB3BDE705B0B81851750C59B" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Employee Stock Ownership Plan Number of Plans</link:label>
    <link:label id="lab_mg_EmployeeStockOwnershipPlanNumberOfPlans_71349FF1AB3BDE705B0B81851750C59B_documentation_en-US" xlink:label="lab_mg_EmployeeStockOwnershipPlanNumberOfPlans_71349FF1AB3BDE705B0B81851750C59B" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Represents the number of plans in connection with the employee stock ownership plan.</link:label>
    <link:loc xlink:href="mg-20181231.xsd#mg_EmployeeStockOwnershipPlanNumberOfPlans" xlink:label="loc_mg_EmployeeStockOwnershipPlanNumberOfPlans_71349FF1AB3BDE705B0B81851750C59B" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_mg_EmployeeStockOwnershipPlanNumberOfPlans_71349FF1AB3BDE705B0B81851750C59B" xlink:to="lab_mg_EmployeeStockOwnershipPlanNumberOfPlans_71349FF1AB3BDE705B0B81851750C59B" xlink:type="arc" />
    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_56D0D95706E44BFBA894818517515C0B_terseLabel_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_56D0D95706E44BFBA894818517515C0B" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Number of awards available for future grants (in shares)</link:label>
    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_56D0D95706E44BFBA894818517515C0B_label_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_56D0D95706E44BFBA894818517515C0B" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_56D0D95706E44BFBA894818517515C0B" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_56D0D95706E44BFBA894818517515C0B" xlink:to="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_56D0D95706E44BFBA894818517515C0B" xlink:type="arc" />
    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_5B9BDE4CD9D84003ED37818517512BD6_terseLabel_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_5B9BDE4CD9D84003ED37818517512BD6" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Stock options outstanding (in shares)</link:label>
    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_5B9BDE4CD9D84003ED37818517512BD6_label_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_5B9BDE4CD9D84003ED37818517512BD6" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_5B9BDE4CD9D84003ED37818517512BD6" xlink:type="locator" />
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    <link:label id="lab_us-gaap_FairValueDisclosuresAbstract_4D5B94AF189F2EECB0960EB895547BF3_label_en-US" xlink:label="lab_us-gaap_FairValueDisclosuresAbstract_4D5B94AF189F2EECB0960EB895547BF3" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Fair Value Disclosures [Abstract]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueDisclosuresAbstract" xlink:label="loc_us-gaap_FairValueDisclosuresAbstract_4D5B94AF189F2EECB0960EB895547BF3" xlink:type="locator" />
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    <link:label id="lab_us-gaap_FairValueLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTableTextBlock_DED481D968BA9BB68AC90EB89554BF2D_terseLabel_en-US" xlink:label="lab_us-gaap_FairValueLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTableTextBlock_DED481D968BA9BB68AC90EB89554BF2D" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Schedule of Changes in Fair Value Level 3 Contingent Consideration</link:label>
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    <link:label id="lab_us-gaap_ScheduleOfCapitalLeasedAsssetsTable_9FAFB9F6DA0908A142443487FB9D81C0_terseLabel_en-US" xlink:label="lab_us-gaap_ScheduleOfCapitalLeasedAsssetsTable_9FAFB9F6DA0908A142443487FB9D81C0" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Schedule of Capital Leased Assets [Table]</link:label>
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    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfCapitalLeasedAsssetsTable" xlink:label="loc_us-gaap_ScheduleOfCapitalLeasedAsssetsTable_9FAFB9F6DA0908A142443487FB9D81C0" xlink:type="locator" />
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    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_CapitalLeasedAssetsLineItems_C6F25074508215CB028E3487FBA08512" xlink:to="lab_us-gaap_CapitalLeasedAssetsLineItems_C6F25074508215CB028E3487FBA08512" xlink:type="arc" />
    <link:label id="lab_mg_CapitalLeaseObligationsRequiredMonthlyPayments_BA8B36739334851F8B1D3487FBAD5C8D_terseLabel_en-US" xlink:label="lab_mg_CapitalLeaseObligationsRequiredMonthlyPayments_BA8B36739334851F8B1D3487FBAD5C8D" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Required monthly payments</link:label>
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    <link:label id="lab_mg_CapitalLeaseObligationsRequiredMonthlyPayments_BA8B36739334851F8B1D3487FBAD5C8D_documentation_en-US" xlink:label="lab_mg_CapitalLeaseObligationsRequiredMonthlyPayments_BA8B36739334851F8B1D3487FBAD5C8D" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Represents the amount required to be paid on a monthly basis under the capital lease obligations.</link:label>
    <link:loc xlink:href="mg-20181231.xsd#mg_CapitalLeaseObligationsRequiredMonthlyPayments" xlink:label="loc_mg_CapitalLeaseObligationsRequiredMonthlyPayments_BA8B36739334851F8B1D3487FBAD5C8D" xlink:type="locator" />
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    <link:label id="lab_us-gaap_RelatedPartyTransactionLineItems_CDA9DABC6F1CCBCB3B52749C52C6191B_terseLabel_en-US" xlink:label="lab_us-gaap_RelatedPartyTransactionLineItems_CDA9DABC6F1CCBCB3B52749C52C6191B" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Related Party Transactions</link:label>
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    <link:label id="lab_us-gaap_StockRepurchaseProgramNumberOfSharesAuthorizedToBeRepurchased_33AC00311701E3AEA376749C52C7100A_terseLabel_en-US" xlink:label="lab_us-gaap_StockRepurchaseProgramNumberOfSharesAuthorizedToBeRepurchased_33AC00311701E3AEA376749C52C7100A" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Number of shares authorized to be repurchased (in shares)</link:label>
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    <link:label id="lab_mg_RelatedPartyTransactionRentPayments_F5AC03C68A62D619FE92749C52C781B0_terseLabel_en-US" xlink:label="lab_mg_RelatedPartyTransactionRentPayments_F5AC03C68A62D619FE92749C52C781B0" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Total rent payments</link:label>
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    <link:label id="lab_mg_RelatedPartyTransactionRentPayments_F5AC03C68A62D619FE92749C52C781B0_documentation_en-US" xlink:label="lab_mg_RelatedPartyTransactionRentPayments_F5AC03C68A62D619FE92749C52C781B0" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Represents the amount of rent paid to related parties under the lease.</link:label>
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    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_CFCCA4CE9CD042B1C84E59EFAB2C427E_terseLabel_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_CFCCA4CE9CD042B1C84E59EFAB2C427E" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Common Stock Options (shares)</link:label>
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    <link:label id="lab_us-gaap_PropertyPlantAndEquipmentTypeDomain_0CED6FEEA91449CDE5F58185180855C0_label_en-US" xlink:label="lab_us-gaap_PropertyPlantAndEquipmentTypeDomain_0CED6FEEA91449CDE5F58185180855C0" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Property, Plant and Equipment, Type [Domain]</link:label>
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    <link:label id="lab_us-gaap_LandMember_9B367AF672360EB1E4E68185180884A8_terseLabel_en-US" xlink:label="lab_us-gaap_LandMember_9B367AF672360EB1E4E68185180884A8" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Land</link:label>
    <link:label id="lab_us-gaap_LandMember_9B367AF672360EB1E4E68185180884A8_label_en-US" xlink:label="lab_us-gaap_LandMember_9B367AF672360EB1E4E68185180884A8" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Land [Member]</link:label>
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    <link:label id="lab_us-gaap_BuildingAndBuildingImprovementsMember_EBE6B196641201BC893A818518089540_terseLabel_en-US" xlink:label="lab_us-gaap_BuildingAndBuildingImprovementsMember_EBE6B196641201BC893A818518089540" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Building and improvements</link:label>
    <link:label id="lab_us-gaap_BuildingAndBuildingImprovementsMember_EBE6B196641201BC893A818518089540_label_en-US" xlink:label="lab_us-gaap_BuildingAndBuildingImprovementsMember_EBE6B196641201BC893A818518089540" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Building and Building Improvements [Member]</link:label>
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    <link:label id="lab_mg_OfficeFurnitureAndEquipmentMember_E9307B8811CEFCF10C88818518083EB6_terseLabel_en-US" xlink:label="lab_mg_OfficeFurnitureAndEquipmentMember_E9307B8811CEFCF10C88818518083EB6" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Office furniture and equipment</link:label>
    <link:label id="lab_mg_OfficeFurnitureAndEquipmentMember_E9307B8811CEFCF10C88818518083EB6_label_en-US" xlink:label="lab_mg_OfficeFurnitureAndEquipmentMember_E9307B8811CEFCF10C88818518083EB6" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Office Furniture and Equipment [Member]</link:label>
    <link:label id="lab_mg_OfficeFurnitureAndEquipmentMember_E9307B8811CEFCF10C88818518083EB6_documentation_en-US" xlink:label="lab_mg_OfficeFurnitureAndEquipmentMember_E9307B8811CEFCF10C88818518083EB6" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Furniture and equipment commonly used in offices and stores that have no permanent connection to the structure of a building or utilities.</link:label>
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    <link:label id="lab_us-gaap_MachineryAndEquipmentMember_B5C7F73BCB119C6FFE5C818518098551_terseLabel_en-US" xlink:label="lab_us-gaap_MachineryAndEquipmentMember_B5C7F73BCB119C6FFE5C818518098551" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Machinery and equipment</link:label>
    <link:label id="lab_us-gaap_MachineryAndEquipmentMember_B5C7F73BCB119C6FFE5C818518098551_label_en-US" xlink:label="lab_us-gaap_MachineryAndEquipmentMember_B5C7F73BCB119C6FFE5C818518098551" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Machinery and Equipment [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MachineryAndEquipmentMember" xlink:label="loc_us-gaap_MachineryAndEquipmentMember_B5C7F73BCB119C6FFE5C818518098551" xlink:type="locator" />
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    <link:label id="lab_us-gaap_PropertyPlantAndEquipmentLineItems_38C9E413AB424DB25C708185180ADE84_terseLabel_en-US" xlink:label="lab_us-gaap_PropertyPlantAndEquipmentLineItems_38C9E413AB424DB25C708185180ADE84" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Property, Plant and Equipment, net</link:label>
    <link:label id="lab_us-gaap_PropertyPlantAndEquipmentLineItems_38C9E413AB424DB25C708185180ADE84_label_en-US" xlink:label="lab_us-gaap_PropertyPlantAndEquipmentLineItems_38C9E413AB424DB25C708185180ADE84" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Property, Plant and Equipment [Line Items]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PropertyPlantAndEquipmentLineItems" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_38C9E413AB424DB25C708185180ADE84" xlink:type="locator" />
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    <link:label id="lab_us-gaap_PropertyPlantAndEquipmentUsefulLife_8AE2DBA682F765BAFDBD8185180AD3FE_terseLabel_en-US" xlink:label="lab_us-gaap_PropertyPlantAndEquipmentUsefulLife_8AE2DBA682F765BAFDBD8185180AD3FE" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Useful Life</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PropertyPlantAndEquipmentUsefulLife" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_8AE2DBA682F765BAFDBD8185180AD3FE" xlink:type="locator" />
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    <link:label id="lab_us-gaap_PropertyPlantAndEquipmentGross_4B7E9A25D7CEABD5DE748185180A8605_terseLabel_en-US" xlink:label="lab_us-gaap_PropertyPlantAndEquipmentGross_4B7E9A25D7CEABD5DE748185180A8605" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Property, plant and equipment, gross</link:label>
    <link:label id="lab_us-gaap_PropertyPlantAndEquipmentGross_4B7E9A25D7CEABD5DE748185180A8605_label_en-US" xlink:label="lab_us-gaap_PropertyPlantAndEquipmentGross_4B7E9A25D7CEABD5DE748185180A8605" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Property, Plant and Equipment, Gross</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PropertyPlantAndEquipmentGross" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_4B7E9A25D7CEABD5DE748185180A8605" xlink:type="locator" />
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    <link:label id="lab_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_FC12BF2563CF4AAEF07E8185180A2067_negatedLabel_en-US" xlink:label="lab_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_FC12BF2563CF4AAEF07E8185180A2067" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:type="resource" xml:lang="en-US">Accumulated depreciation and amortization</link:label>
    <link:label id="lab_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_FC12BF2563CF4AAEF07E8185180A2067_label_en-US" xlink:label="lab_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_FC12BF2563CF4AAEF07E8185180A2067" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_FC12BF2563CF4AAEF07E8185180A2067" xlink:type="locator" />
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    <link:label id="lab_us-gaap_PropertyPlantAndEquipmentNet_1C4AAF0C6E9EE898EE5A8185180B46BB_totalLabel_en-US" xlink:label="lab_us-gaap_PropertyPlantAndEquipmentNet_1C4AAF0C6E9EE898EE5A8185180B46BB" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xml:lang="en-US">Property, plant and equipment, net</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_1C4AAF0C6E9EE898EE5A8185180B46BB" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentNet_1C4AAF0C6E9EE898EE5A8185180B46BB" xlink:to="lab_us-gaap_PropertyPlantAndEquipmentNet_1C4AAF0C6E9EE898EE5A8185180B46BB" xlink:type="arc" />
    <link:label id="lab_us-gaap_Depreciation_916E56859E3339CDAEA38185180B7C50_terseLabel_en-US" xlink:label="lab_us-gaap_Depreciation_916E56859E3339CDAEA38185180B7C50" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Depreciation expense</link:label>
    <link:label id="lab_us-gaap_Depreciation_916E56859E3339CDAEA38185180B7C50_label_en-US" xlink:label="lab_us-gaap_Depreciation_916E56859E3339CDAEA38185180B7C50" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Depreciation</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_Depreciation" xlink:label="loc_us-gaap_Depreciation_916E56859E3339CDAEA38185180B7C50" xlink:type="locator" />
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    <link:label id="lab_us-gaap_CapitalLeasesFutureMinimumPaymentsDueCurrent_1E38F6B57F5B8D1002D33470526B86EE_terseLabel_en-US" xlink:label="lab_us-gaap_CapitalLeasesFutureMinimumPaymentsDueCurrent_1E38F6B57F5B8D1002D33470526B86EE" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">2019</link:label>
    <link:label id="lab_us-gaap_CapitalLeasesFutureMinimumPaymentsDueCurrent_1E38F6B57F5B8D1002D33470526B86EE_label_en-US" xlink:label="lab_us-gaap_CapitalLeasesFutureMinimumPaymentsDueCurrent_1E38F6B57F5B8D1002D33470526B86EE" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Capital Leases, Future Minimum Payments Due, Next Twelve Months</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CapitalLeasesFutureMinimumPaymentsDueCurrent" xlink:label="loc_us-gaap_CapitalLeasesFutureMinimumPaymentsDueCurrent_1E38F6B57F5B8D1002D33470526B86EE" xlink:type="locator" />
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    <link:label id="lab_us-gaap_CapitalLeasesFutureMinimumPaymentsDueInTwoYears_817D29133F3791B540663470526B7E61_terseLabel_en-US" xlink:label="lab_us-gaap_CapitalLeasesFutureMinimumPaymentsDueInTwoYears_817D29133F3791B540663470526B7E61" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">2020</link:label>
    <link:label id="lab_us-gaap_CapitalLeasesFutureMinimumPaymentsDueInTwoYears_817D29133F3791B540663470526B7E61_label_en-US" xlink:label="lab_us-gaap_CapitalLeasesFutureMinimumPaymentsDueInTwoYears_817D29133F3791B540663470526B7E61" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Capital Leases, Future Minimum Payments Due in Two Years</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CapitalLeasesFutureMinimumPaymentsDueInTwoYears" xlink:label="loc_us-gaap_CapitalLeasesFutureMinimumPaymentsDueInTwoYears_817D29133F3791B540663470526B7E61" xlink:type="locator" />
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    <link:label id="lab_us-gaap_CapitalLeasesFutureMinimumPaymentsDueInThreeYears_D7621A52FAF9CA2D592C3470526BF958_terseLabel_en-US" xlink:label="lab_us-gaap_CapitalLeasesFutureMinimumPaymentsDueInThreeYears_D7621A52FAF9CA2D592C3470526BF958" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">2021</link:label>
    <link:label id="lab_us-gaap_CapitalLeasesFutureMinimumPaymentsDueInThreeYears_D7621A52FAF9CA2D592C3470526BF958_label_en-US" xlink:label="lab_us-gaap_CapitalLeasesFutureMinimumPaymentsDueInThreeYears_D7621A52FAF9CA2D592C3470526BF958" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Capital Leases, Future Minimum Payments Due in Three Years</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CapitalLeasesFutureMinimumPaymentsDueInThreeYears" xlink:label="loc_us-gaap_CapitalLeasesFutureMinimumPaymentsDueInThreeYears_D7621A52FAF9CA2D592C3470526BF958" xlink:type="locator" />
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    <link:label id="lab_us-gaap_MultiemployerPlansPensionMember_2B4CC576356469D0E01D34CF033936B7_terseLabel_en-US" xlink:label="lab_us-gaap_MultiemployerPlansPensionMember_2B4CC576356469D0E01D34CF033936B7" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Multiemployer Plans, Pension</link:label>
    <link:label id="lab_us-gaap_MultiemployerPlansPensionMember_2B4CC576356469D0E01D34CF033936B7_label_en-US" xlink:label="lab_us-gaap_MultiemployerPlansPensionMember_2B4CC576356469D0E01D34CF033936B7" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Multiemployer Plans, Pension [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MultiemployerPlansPensionMember" xlink:label="loc_us-gaap_MultiemployerPlansPensionMember_2B4CC576356469D0E01D34CF033936B7" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_MultiemployerPlansPensionMember_2B4CC576356469D0E01D34CF033936B7" xlink:to="lab_us-gaap_MultiemployerPlansPensionMember_2B4CC576356469D0E01D34CF033936B7" xlink:type="arc" />
    <link:label id="lab_us-gaap_MultiemployerPlanNameAxis_B0698AA0E8A7C090432034CF033AD859_terseLabel_en-US" xlink:label="lab_us-gaap_MultiemployerPlanNameAxis_B0698AA0E8A7C090432034CF033AD859" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Multiemployer Plan Name [Axis]</link:label>
    <link:label id="lab_us-gaap_MultiemployerPlanNameAxis_B0698AA0E8A7C090432034CF033AD859_label_en-US" xlink:label="lab_us-gaap_MultiemployerPlanNameAxis_B0698AA0E8A7C090432034CF033AD859" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Multiemployer Plan Name [Axis]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MultiemployerPlanNameAxis" xlink:label="loc_us-gaap_MultiemployerPlanNameAxis_B0698AA0E8A7C090432034CF033AD859" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_MultiemployerPlanNameAxis_B0698AA0E8A7C090432034CF033AD859" xlink:to="lab_us-gaap_MultiemployerPlanNameAxis_B0698AA0E8A7C090432034CF033AD859" xlink:type="arc" />
    <link:label id="lab_us-gaap_MultiemployerPlanNameDomain_263BEBF37F48C38E221934CF033A5367_terseLabel_en-US" xlink:label="lab_us-gaap_MultiemployerPlanNameDomain_263BEBF37F48C38E221934CF033A5367" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Multiemployer Plan Name [Domain]</link:label>
    <link:label id="lab_us-gaap_MultiemployerPlanNameDomain_263BEBF37F48C38E221934CF033A5367_label_en-US" xlink:label="lab_us-gaap_MultiemployerPlanNameDomain_263BEBF37F48C38E221934CF033A5367" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Multiemployer Plan Name [Domain]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MultiemployerPlanNameDomain" xlink:label="loc_us-gaap_MultiemployerPlanNameDomain_263BEBF37F48C38E221934CF033A5367" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_MultiemployerPlanNameDomain_263BEBF37F48C38E221934CF033A5367" xlink:to="lab_us-gaap_MultiemployerPlanNameDomain_263BEBF37F48C38E221934CF033A5367" xlink:type="arc" />
    <link:label id="lab_mg_BoilermakersandPipefittersPlansMember_4989AD55D07E5C9F65EC34CF033B7CE5_terseLabel_en-US" xlink:label="lab_mg_BoilermakersandPipefittersPlansMember_4989AD55D07E5C9F65EC34CF033B7CE5" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Boilermakers and Pipefitters Plans</link:label>
    <link:label id="lab_mg_BoilermakersandPipefittersPlansMember_4989AD55D07E5C9F65EC34CF033B7CE5_label_en-US" xlink:label="lab_mg_BoilermakersandPipefittersPlansMember_4989AD55D07E5C9F65EC34CF033B7CE5" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Boilermakers and Pipefitters Plans [Member]</link:label>
    <link:label id="lab_mg_BoilermakersandPipefittersPlansMember_4989AD55D07E5C9F65EC34CF033B7CE5_documentation_en-US" xlink:label="lab_mg_BoilermakersandPipefittersPlansMember_4989AD55D07E5C9F65EC34CF033B7CE5" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Boilermakers and Pipefitters Plans</link:label>
    <link:loc xlink:href="mg-20181231.xsd#mg_BoilermakersandPipefittersPlansMember" xlink:label="loc_mg_BoilermakersandPipefittersPlansMember_4989AD55D07E5C9F65EC34CF033B7CE5" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_mg_BoilermakersandPipefittersPlansMember_4989AD55D07E5C9F65EC34CF033B7CE5" xlink:to="lab_mg_BoilermakersandPipefittersPlansMember_4989AD55D07E5C9F65EC34CF033B7CE5" xlink:type="arc" />
    <link:label id="lab_us-gaap_MultiemployerPlansLineItems_BDAD78772DF19A59C1ED34CF033BC3DF_terseLabel_en-US" xlink:label="lab_us-gaap_MultiemployerPlansLineItems_BDAD78772DF19A59C1ED34CF033BC3DF" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Multiemployer Plans [Line Items]</link:label>
    <link:label id="lab_us-gaap_MultiemployerPlansLineItems_BDAD78772DF19A59C1ED34CF033BC3DF_label_en-US" xlink:label="lab_us-gaap_MultiemployerPlansLineItems_BDAD78772DF19A59C1ED34CF033BC3DF" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Multiemployer Plans [Line Items]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MultiemployerPlansLineItems" xlink:label="loc_us-gaap_MultiemployerPlansLineItems_BDAD78772DF19A59C1ED34CF033BC3DF" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_MultiemployerPlansLineItems_BDAD78772DF19A59C1ED34CF033BC3DF" xlink:to="lab_us-gaap_MultiemployerPlansLineItems_BDAD78772DF19A59C1ED34CF033BC3DF" xlink:type="arc" />
    <link:label id="lab_us-gaap_DefinedContributionPensionAndOtherPostretirementPlansDisclosureAbstract_1AC4BD0B2A0165E7FD6134CF033BAEF4_terseLabel_en-US" xlink:label="lab_us-gaap_DefinedContributionPensionAndOtherPostretirementPlansDisclosureAbstract_1AC4BD0B2A0165E7FD6134CF033BAEF4" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">401(k) savings plan</link:label>
    <link:label id="lab_us-gaap_DefinedContributionPensionAndOtherPostretirementPlansDisclosureAbstract_1AC4BD0B2A0165E7FD6134CF033BAEF4_label_en-US" xlink:label="lab_us-gaap_DefinedContributionPensionAndOtherPostretirementPlansDisclosureAbstract_1AC4BD0B2A0165E7FD6134CF033BAEF4" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Defined Contribution Plan [Abstract]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedContributionPensionAndOtherPostretirementPlansDisclosureAbstract" xlink:label="loc_us-gaap_DefinedContributionPensionAndOtherPostretirementPlansDisclosureAbstract_1AC4BD0B2A0165E7FD6134CF033BAEF4" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DefinedContributionPensionAndOtherPostretirementPlansDisclosureAbstract_1AC4BD0B2A0165E7FD6134CF033BAEF4" xlink:to="lab_us-gaap_DefinedContributionPensionAndOtherPostretirementPlansDisclosureAbstract_1AC4BD0B2A0165E7FD6134CF033BAEF4" xlink:type="arc" />
    <link:label id="lab_mg_DefinedContributionPlanMinimumAgeForEmployeesToContributeCatchUpContributionsUnderIRSLimits_6E460F1C0A9C095B81C934CF033B22F9_terseLabel_en-US" xlink:label="lab_mg_DefinedContributionPlanMinimumAgeForEmployeesToContributeCatchUpContributionsUnderIRSLimits_6E460F1C0A9C095B81C934CF033B22F9" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Minimum age for employees to contribute catch up contributions under IRS limits</link:label>
    <link:label id="lab_mg_DefinedContributionPlanMinimumAgeForEmployeesToContributeCatchUpContributionsUnderIRSLimits_6E460F1C0A9C095B81C934CF033B22F9_label_en-US" xlink:label="lab_mg_DefinedContributionPlanMinimumAgeForEmployeesToContributeCatchUpContributionsUnderIRSLimits_6E460F1C0A9C095B81C934CF033B22F9" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Defined Contribution Plan Minimum Age for Employees to Contribute Catch Up Contributions Under IRS Limits</link:label>
    <link:label id="lab_mg_DefinedContributionPlanMinimumAgeForEmployeesToContributeCatchUpContributionsUnderIRSLimits_6E460F1C0A9C095B81C934CF033B22F9_documentation_en-US" xlink:label="lab_mg_DefinedContributionPlanMinimumAgeForEmployeesToContributeCatchUpContributionsUnderIRSLimits_6E460F1C0A9C095B81C934CF033B22F9" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Represents the minimum age for employees to contribute catch up contributions under IRS limits.</link:label>
    <link:loc xlink:href="mg-20181231.xsd#mg_DefinedContributionPlanMinimumAgeForEmployeesToContributeCatchUpContributionsUnderIRSLimits" xlink:label="loc_mg_DefinedContributionPlanMinimumAgeForEmployeesToContributeCatchUpContributionsUnderIRSLimits_6E460F1C0A9C095B81C934CF033B22F9" xlink:type="locator" />
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    <link:label id="lab_mg_DefinedContributionPlanContinuousServicePeriodAfterWhichEmployeesBecomeEligibleToParticipateUnderPlan_B0237D228E8AE86BB22A34CF033CDA04_terseLabel_en-US" xlink:label="lab_mg_DefinedContributionPlanContinuousServicePeriodAfterWhichEmployeesBecomeEligibleToParticipateUnderPlan_B0237D228E8AE86BB22A34CF033CDA04" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Continuous service period required for eligibility of employees to participate under the plan</link:label>
    <link:label id="lab_mg_DefinedContributionPlanContinuousServicePeriodAfterWhichEmployeesBecomeEligibleToParticipateUnderPlan_B0237D228E8AE86BB22A34CF033CDA04_label_en-US" xlink:label="lab_mg_DefinedContributionPlanContinuousServicePeriodAfterWhichEmployeesBecomeEligibleToParticipateUnderPlan_B0237D228E8AE86BB22A34CF033CDA04" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Defined Contribution Plan, Continuous Service Period after which Employees become Eligible to Participate under Plan</link:label>
    <link:label id="lab_mg_DefinedContributionPlanContinuousServicePeriodAfterWhichEmployeesBecomeEligibleToParticipateUnderPlan_B0237D228E8AE86BB22A34CF033CDA04_documentation_en-US" xlink:label="lab_mg_DefinedContributionPlanContinuousServicePeriodAfterWhichEmployeesBecomeEligibleToParticipateUnderPlan_B0237D228E8AE86BB22A34CF033CDA04" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Represents the continuous service period required for eligibility of employees to participate under the plan.</link:label>
    <link:loc xlink:href="mg-20181231.xsd#mg_DefinedContributionPlanContinuousServicePeriodAfterWhichEmployeesBecomeEligibleToParticipateUnderPlan" xlink:label="loc_mg_DefinedContributionPlanContinuousServicePeriodAfterWhichEmployeesBecomeEligibleToParticipateUnderPlan_B0237D228E8AE86BB22A34CF033CDA04" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_mg_DefinedContributionPlanContinuousServicePeriodAfterWhichEmployeesBecomeEligibleToParticipateUnderPlan_B0237D228E8AE86BB22A34CF033CDA04" xlink:to="lab_mg_DefinedContributionPlanContinuousServicePeriodAfterWhichEmployeesBecomeEligibleToParticipateUnderPlan_B0237D228E8AE86BB22A34CF033CDA04" xlink:type="arc" />
    <link:label id="lab_us-gaap_DefinedContributionPlanEmployerMatchingContributionPercentOfMatch_4C7421EE4D4127E589A634CF033C960A_terseLabel_en-US" xlink:label="lab_us-gaap_DefinedContributionPlanEmployerMatchingContributionPercentOfMatch_4C7421EE4D4127E589A634CF033C960A" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Maximum Company match amount of employee contributions matched up to 6% of annual compensation (as a percent)</link:label>
    <link:label id="lab_us-gaap_DefinedContributionPlanEmployerMatchingContributionPercentOfMatch_4C7421EE4D4127E589A634CF033C960A_label_en-US" xlink:label="lab_us-gaap_DefinedContributionPlanEmployerMatchingContributionPercentOfMatch_4C7421EE4D4127E589A634CF033C960A" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Defined Contribution Plan, Employer Matching Contribution, Percent of Match</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedContributionPlanEmployerMatchingContributionPercentOfMatch" xlink:label="loc_us-gaap_DefinedContributionPlanEmployerMatchingContributionPercentOfMatch_4C7421EE4D4127E589A634CF033C960A" xlink:type="locator" />
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    <link:label id="lab_us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent_08659950ED932BBEF0C034CF033C8414_terseLabel_en-US" xlink:label="lab_us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent_08659950ED932BBEF0C034CF033C8414" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Maximum percentage of employee's annual compensation for which the company contributes a matching contribution (as a percent)</link:label>
    <link:label id="lab_us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent_08659950ED932BBEF0C034CF033C8414_label_en-US" xlink:label="lab_us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent_08659950ED932BBEF0C034CF033C8414" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent" xlink:label="loc_us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent_08659950ED932BBEF0C034CF033C8414" xlink:type="locator" />
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    <link:label id="lab_mg_DefinedContributionPlanEmployersMatchingContributionAnnualVestingPeriod_A7A8FF5EC0C6C07D4AA734CF033CF548_terseLabel_en-US" xlink:label="lab_mg_DefinedContributionPlanEmployersMatchingContributionAnnualVestingPeriod_A7A8FF5EC0C6C07D4AA734CF033CF548" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Vesting period for employer matching contribution</link:label>
    <link:label id="lab_mg_DefinedContributionPlanEmployersMatchingContributionAnnualVestingPeriod_A7A8FF5EC0C6C07D4AA734CF033CF548_label_en-US" xlink:label="lab_mg_DefinedContributionPlanEmployersMatchingContributionAnnualVestingPeriod_A7A8FF5EC0C6C07D4AA734CF033CF548" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Defined Contribution Plan Employers Matching Contribution Annual Vesting Period</link:label>
    <link:label id="lab_mg_DefinedContributionPlanEmployersMatchingContributionAnnualVestingPeriod_A7A8FF5EC0C6C07D4AA734CF033CF548_documentation_en-US" xlink:label="lab_mg_DefinedContributionPlanEmployersMatchingContributionAnnualVestingPeriod_A7A8FF5EC0C6C07D4AA734CF033CF548" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Represents the vesting period for employer matching contribution under the plan.</link:label>
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    <link:label id="lab_us-gaap_DefinedContributionPlanCostRecognized_90FDC05E28006907539834CF033CA11D_terseLabel_en-US" xlink:label="lab_us-gaap_DefinedContributionPlanCostRecognized_90FDC05E28006907539834CF033CA11D" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Contribution under 401(k) savings plan</link:label>
    <link:label id="lab_us-gaap_DefinedContributionPlanCostRecognized_90FDC05E28006907539834CF033CA11D_label_en-US" xlink:label="lab_us-gaap_DefinedContributionPlanCostRecognized_90FDC05E28006907539834CF033CA11D" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Defined Contribution Plan, Cost</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedContributionPlanCostRecognized" xlink:label="loc_us-gaap_DefinedContributionPlanCostRecognized_90FDC05E28006907539834CF033CA11D" xlink:type="locator" />
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    <link:label id="lab_us-gaap_MultiemployerPlansAbstract_11C289969A1545E3903A34CF033C1D31_terseLabel_en-US" xlink:label="lab_us-gaap_MultiemployerPlansAbstract_11C289969A1545E3903A34CF033C1D31" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Multiemployer Defined Benefit Pension Plans</link:label>
    <link:label id="lab_us-gaap_MultiemployerPlansAbstract_11C289969A1545E3903A34CF033C1D31_label_en-US" xlink:label="lab_us-gaap_MultiemployerPlansAbstract_11C289969A1545E3903A34CF033C1D31" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Multiemployer Plans [Abstract]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MultiemployerPlansAbstract" xlink:label="loc_us-gaap_MultiemployerPlansAbstract_11C289969A1545E3903A34CF033C1D31" xlink:type="locator" />
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    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_0D17ED5844D5EF09B02F59EFAB0AE0A3_terseLabel_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_0D17ED5844D5EF09B02F59EFAB0AE0A3" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Restricted stock awards vested</link:label>
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    <link:label id="lab_us-gaap_ConcentrationRiskPercentage1_67629E49256DCFF203E67E0503E3B129_terseLabel_en-US" xlink:label="lab_us-gaap_ConcentrationRiskPercentage1_67629E49256DCFF203E67E0503E3B129" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Percentage of concentration risk</link:label>
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