Represent the minimum interest coverage ratio under the credit agreement.

No definition available.

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Namespace Prefix:	myrg_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	duration

- Definition

Threshold of debt coverage ration at which the credit agreement restricts certain types of payments.

+ References

No definition available.

+ Details

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Namespace Prefix:	myrg_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of debt instruments.

+ References

No definition available.

+ Details

Name:	myrg_DebtInstrumentNumberOfDebtInstruments
Namespace Prefix:	myrg_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

The Company has the option to expand the debt coverage ratio in the event of an acquisition.

+ References

No definition available.

+ Details

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Namespace Prefix:	myrg_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	duration

- Definition

The Company has the option to expand the debt coverage ratio to 3.5 in the event of an acquisition in excess of $30 million. The expansion occurs in the quarter the acquisition is consummated and shall continue in effect for the next four consecutive quarters.

+ References

No definition available.

+ Details

Name:	myrg_LeverageCoverageRatioExpansion
Namespace Prefix:	myrg_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the option to increase maximum borrowings on the credit facility.

+ References

No definition available.

+ Details

Name:	myrg_LineOfCreditFacilityOptionToIncreaseMaximumBorrowingCapacity
Namespace Prefix:	myrg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Maximum consideration for acquisitions under the credit agreement allows the expansion of the Leverage Ratio.

+ References

No definition available.

+ Details

Name:	myrg_MaximumAcquisitionConsiderationUnderCreditAgreement
Namespace Prefix:	myrg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Percentage of capital stock from direct foreign subsidiaries pledged as collateral for a debt.

+ References

No definition available.

+ Details

Name:	myrg_PercentageOfCapitalStockFromDirectForeignSubsidiaries
Namespace Prefix:	myrg_
Data Type:	num:percentItemType
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

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, after accumulated amortization, of debt issuance costs related to line of credit arrangements. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section S45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=68176171&loc=SL68176184-208336

+ Details

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

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

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

- Definition

The fee, expressed as a percentage of the line of credit facility, for the line of credit facility regardless of whether the facility has been used.

+ References

No definition available.

+ Details

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

- Definition

The effective interest rate during the reporting period.

+ 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:	num:percentItemType
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

+ Details

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

- Definition

The fee, expressed as a percentage of the line of credit facility, for available but unused credit capacity under the credit facility.

+ References

No definition available.

+ Details

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

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=myrg_CreditAgreementMember
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Balance Type:
Period Type:

- Details

Name:	srt_CurrencyAxis=currency_CAD
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Data Type:	na
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Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_LetterOfCreditMember
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Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByLiabilityClassAxis=myrg_InsuranceProgramObligationsMember
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Data Type:	na
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Period Type:

- Details

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- Details

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- Details

Name:	us-gaap_DebtInstrumentAxis=myrg_MasterLoanAgreementMember
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Debt - Narrative (Details) $ in Millions		3 Months Ended
Debt - Narrative (Details) $ in Millions	Jun. 30, 2016 USD ($)	Mar. 31, 2019 USD ($) equipment-note	Dec. 31, 2018 USD ($)	Sep. 28, 2018 USD ($)
Secured Debt [Member] \| Credit Agreement [Member]
Debt Instrument [Line Items]
Option to increase borrowing capacity	$ 100.0
Maximum borrowing capacity	$ 250.0
Interest coverage ratio		3.0
Percentage of capital stock from direct foreign subsidiaries	65.00%
Maximum acquisition consideration under credit agreement		$ 50.0
Deferred debt issuance costs		$ 0.6
Debt instrument covenant leveraged debt ratio restriction		2.25
Leverage coverage ratio expansion		3.5
Leverage coverage ratio		3.0
Debt instrument term	5 years
Interest rate on borrowings outstanding		3.51%
Secured Debt [Member] \| Credit Agreement [Member] \| Canada, Dollars [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 50.0
Secured Debt [Member] \| Credit Agreement [Member] \| Letter of Credit [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity				$ 150.0
Letters of credit outstanding		$ 21.2	$ 21.2
Secured Debt [Member] \| Credit Agreement [Member] \| Letter of Credit [Member] \| Insurance Program Obligations [Member]
Debt Instrument [Line Items]
Letters of credit outstanding		17.6	17.6
Secured Debt [Member] \| Credit Agreement [Member] \| Letter of Credit [Member] \| Contract Performance Obligations [Member]
Debt Instrument [Line Items]
Letters of credit outstanding		$ 3.6	$ 3.6
Secured Debt [Member] \| Credit Agreement [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Commitment fee on unused capacity		0.375%
Secured Debt [Member] \| Credit Agreement [Member] \| Maximum [Member] \| Performance letters of credit [Member]
Debt Instrument [Line Items]
Letter of credit facility commitment percentage		1.125%
Secured Debt [Member] \| Credit Agreement [Member] \| Maximum [Member] \| Non-performance Letters Of Credit [Member]
Debt Instrument [Line Items]
Letter of credit facility commitment percentage		2.125%
Secured Debt [Member] \| Credit Agreement [Member] \| Maximum [Member] \| London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Interest rate margin		2.00%
Secured Debt [Member] \| Credit Agreement [Member] \| Maximum [Member] \| Base Rate [Member]
Debt Instrument [Line Items]
Interest rate margin		1.00%
Secured Debt [Member] \| Credit Agreement [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Commitment fee on unused capacity		0.20%
Secured Debt [Member] \| Credit Agreement [Member] \| Minimum [Member] \| Performance letters of credit [Member]
Debt Instrument [Line Items]
Letter of credit facility commitment percentage		0.625%
Secured Debt [Member] \| Credit Agreement [Member] \| Minimum [Member] \| Non-performance Letters Of Credit [Member]
Debt Instrument [Line Items]
Letter of credit facility commitment percentage		1.125%
Secured Debt [Member] \| Credit Agreement [Member] \| Minimum [Member] \| London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Interest rate margin		1.00%
Secured Debt [Member] \| Credit Agreement [Member] \| Minimum [Member] \| Base Rate [Member]
Debt Instrument [Line Items]
Interest rate margin		0.00%
Notes Payable to Banks [Member] \| Master Loan Agreement [Member]
Debt Instrument [Line Items]
Number of equipment notes (equipment note) \| equipment-note		5