Debt Covenant, Number Of Consecutive Business Days

No definition available.

Name:	mg_DebtCovenantNumberOfConsecutiveBusinessDays
Namespace Prefix:	mg_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt Instrument, Covenant, Amount Deducted From Aggregate Cash and Cash Equivalents Held By Company and Subsidiaries If Prepayment of Credit Facility is Required

+ References

No definition available.

+ Details

Name:	mg_DebtInstrumentCovenantAmountDeductedFromAggregateCashAndCashEquivalentsHeldByCompanyAndSubsidiariesIfPrepaymentOfCreditFacilityIsRequired
Namespace Prefix:	mg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents the Funded Debt Leverage Ratio on which the entity will bear an additional interest on debt.

+ References

No definition available.

+ Details

Name:	mg_DebtInstrumentCovenantFundedDebtLeverageRatioForAdditionalInterestPayment
Namespace Prefix:	mg_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the Interest Coverage Ratio required under the terms of the covenants.

+ References

No definition available.

+ Details

Name:	mg_DebtInstrumentCovenantInterestCoverageRatio
Namespace Prefix:	mg_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt Instrument, Covenant, Minimum EBITDA, Amount

+ References

No definition available.

+ Details

Name:	mg_DebtInstrumentCovenantMinimumEBITDAAmount
Namespace Prefix:	mg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Debt Instrument, Covenant, Prepayment of Outstanding Credit Facility Required if Amount Under the Credit Facility Exceeds, Amount

+ References

No definition available.

+ Details

Name:	mg_DebtInstrumentCovenantPrepaymentOfOutstandingCreditFacilityRequiredIfAmountUnderTheCreditFacilityExceedsAmount
Namespace Prefix:	mg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Debt Instrument, Covenant, Prepayment of Outstanding Credit Facility Required if Cash and Cash Equivalents Exceeds, Amount

+ References

No definition available.

+ Details

Name:	mg_DebtInstrumentCovenantPrepaymentOfOutstandingCreditFacilityRequiredIfCashAndCashEquivalentsExceedsAmount
Namespace Prefix:	mg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Debt Instrument, Covenant, Pro Forma Funded Debt Leverage Ratio due to Business Acquisitions

+ References

No definition available.

+ Details

Name:	mg_DebtInstrumentCovenantProFormaFundedDebtLeverageRatioDueToBusinessAcquisitions
Namespace Prefix:	mg_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt Instrument, Covenant Temporarily Increase in Funded Debt Leverage Ratio due to Business Acquisitions

+ References

No definition available.

+ Details

Name:	mg_DebtInstrumentCovenantTemporarilyIncreaseinFundedDebtLeverageRatioduetoBusinessAcquisitions
Namespace Prefix:	mg_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_RevolvingCreditFacilityMember
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Balance Type:
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- Details

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- Details

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- Details

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- Details

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- Details

Name:	srt_RangeAxis=srt_MaximumMember
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- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
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- Details

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- Details

Name:	us-gaap_DebtInstrumentAxis=mg_CreditAgreementMember
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Balance Type:
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- Details

Name:	mg_DebtCovenantPeriodAxis=mg_DebtCovenantPeriodFiveMember
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- Details

Name:	mg_DebtCovenantPeriodAxis=mg_DebtCovenantPeriodSixMember
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- Details

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- Details

Name:	mg_DebtCovenantPeriodAxis=mg_DebtCovenantPeriodEightMember
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Long-Term Debt - Subsequent Events (Details) - Senior credit facility			3 Months Ended
	May 15, 2020 USD ($) d	Mar. 09, 2020	Mar. 31, 2020 USD ($)
Debt Instrument [Line Items]
Fixed charge coverage ratio			1.25
Maximum borrowing capacity			$ 300,000,000
Quarter ended June 30, 2020
Debt Instrument [Line Items]
Funded debt leverage ratio			4.0
Quarter ended September 30, 2020
Debt Instrument [Line Items]
Funded debt leverage ratio			3.75
Minimum
Debt Instrument [Line Items]
Funded debt leverage ratio for acquisitions			3.5
Minimum \| Quarter ended December 31, 2020
Debt Instrument [Line Items]
Funded debt leverage ratio			3.50
Maximum
Debt Instrument [Line Items]
Funded debt leverage ratio for acquisitions		3.0	4.0
LIBOR \| Minimum
Debt Instrument [Line Items]
Margin percentage			1.00%
LIBOR \| Maximum
Debt Instrument [Line Items]
Margin percentage			2.25%
Subsequent Event \| Credit Agreement
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 175,000,000.0
Amount deducted from aggregate cash and cash equivalents held by company and it's subsidiaries if prepayment of credit facility is required	$ 10,000,000.0
Number of consecutive business days \| d	2
Maximum amount outstanding under the revolving credit facility if prepayment of facility is required	$ 75,000,000.0
Cash and cash equivalents if prepayment of facility is required	$ 10,000,000.0
Subsequent Event \| Credit Agreement \| Quarter ended December 31, 2020
Debt Instrument [Line Items]
Funded debt leverage ratio	5.25
Debt covenant, minimum EBITDA, amount	$ 38,550,000
Subsequent Event \| Credit Agreement \| Quarter ended September 30, 2021 and thereafter
Debt Instrument [Line Items]
Funded debt leverage ratio	3.50
Subsequent Event \| Credit Agreement \| Quarter ended March 31, 2021
Debt Instrument [Line Items]
Fixed charge coverage ratio	1.0
Subsequent Event \| Credit Agreement \| Quarter ended June 30, 2021
Debt Instrument [Line Items]
Fixed charge coverage ratio	1.25
Subsequent Event \| Credit Agreement \| Quarter ended June 30, 2020
Debt Instrument [Line Items]
Debt covenant, minimum EBITDA, amount	$ 3,440,000
Subsequent Event \| Credit Agreement \| Quarter ended September 30, 2020
Debt Instrument [Line Items]
Debt covenant, minimum EBITDA, amount	24,250,000
Subsequent Event \| Credit Agreement \| All times through September 30, 2020
Debt Instrument [Line Items]
Debt covenant, minimum EBITDA, amount	$ 20,000,000.0
Subsequent Event \| Credit Agreement \| Maximum
Debt Instrument [Line Items]
Funded debt leverage ratio for acquisitions	2.50
Pro forma funded debt leverage ratio	3.25
Subsequent Event \| Credit Agreement \| LIBOR
Debt Instrument [Line Items]
Margin percentage	1.00%
Subsequent Event \| Credit Agreement \| LIBOR \| Minimum
Debt Instrument [Line Items]
Margin percentage	1.50%
Subsequent Event \| Credit Agreement \| LIBOR \| Maximum
Debt Instrument [Line Items]
Margin percentage	4.15%