Represent the minimum interest coverage ratio under the credit agreement.

No definition available.

Name:	myrg_DebtInstrumentCovenantInterestCoverageRatio
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

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

- Definition

Represents the fees for the letter of credit facility, expressed as a percentage.

+ References

No definition available.

+ Details

Name:	myrg_LetterOfCreditFeesPercentage
Namespace Prefix:	myrg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

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

+ References

No definition available.

+ Details

Name:	myrg_LeverageCoverageRatio
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

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

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

- Definition

Weighted average interest rate of debt outstanding.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtWeightedAverageInterestRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
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

Date the credit facility first became available, in CCYY-MM-DD format.

+ 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

Name:	us-gaap_LineOfCreditFacilityInitiationDate1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
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

Name:	us-gaap_FairValueByLiabilityClassAxis=myrg_InsuranceProgramObligationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByLiabilityClassAxis=myrg_ContractPerformanceObligationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=myrg_CreditFacilityAmendmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=myrg_PerformanceLettersOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=myrg_NonperformanceLettersOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_BaseRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=myrg_SyndicatedCreditAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=myrg_TwoThousandSixteenCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=myrg_CreditAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=myrg_ForeignRevolvingLoansAndLettersOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Debt (Details Textual) $ in Millions	1 Months Ended	6 Months Ended	9 Months Ended
Debt (Details Textual) $ in Millions	Jun. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)
Debt Instrument [Line Items]
Letters of Credit Outstanding, Amount			$ 21.2	$ 20.9
Debt Issuance Costs, Line of Credit Arrangements, Net			$ 0.6
Debt Instrument Covenant Leveraged Debt Ratio Restriction			2.25
Insurance Program Obligations [Member]
Debt Instrument [Line Items]
Letters of Credit Outstanding, Amount			$ 17.6	17.6
Contract Performance Obligations [Member]
Debt Instrument [Line Items]
Letters of Credit Outstanding, Amount			$ 3.6	$ 3.3
Credit Facility Amendment [Member]
Debt Instrument [Line Items]
Letters of Credit Outstanding, Amount	$ 150.0	$ 150.0
Line of Credit Facility, Initiation Date	Sep. 28, 2018
Maximum [Member]
Debt Instrument [Line Items]
Leverage Coverage Ratio Expansion			3.5
Leverage Coverage Ratio			3.0
Maximum [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage			0.375%
Maximum [Member] \| Performance letters of credit [Member]
Debt Instrument [Line Items]
Letter of credit fee (as a percent)			1.125%
Maximum [Member] \| Non-performance Letters Of Credit [Member]
Debt Instrument [Line Items]
Interest rate margin (as a percent)			2.125%
Maximum [Member] \| London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Interest rate margin (as a percent)			2.00%
Maximum [Member] \| Base Rate [Member]
Debt Instrument [Line Items]
Interest rate margin (as a percent)			1.00%
Minimum [Member]
Debt Instrument [Line Items]
Interest coverage ratio			3.0
Minimum [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage			0.20%
Minimum [Member] \| Performance letters of credit [Member]
Debt Instrument [Line Items]
Letter of credit fee (as a percent)			0.625%
Minimum [Member] \| Non-performance Letters Of Credit [Member]
Debt Instrument [Line Items]
Interest rate margin (as a percent)			1.125%
Minimum [Member] \| London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Interest rate margin (as a percent)			1.00%
Minimum [Member] \| Base Rate [Member]
Debt Instrument [Line Items]
Interest rate margin (as a percent)			0.00%
Syndicated Credit Agreement [Member] \| Facility [Member]
Debt Instrument [Line Items]
Option to increase borrowing capacity		100.0
Maximum borrowing capacity	$ 250.0	$ 250.0
Credit Agreement [Member]
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate			2.90%
Credit Agreement [Member] \| Facility [Member]
Debt Instrument [Line Items]
Percentage of Capital Stock From Direct Foreign Subsidiaries		65.00%
Maximum Acquisition Consideration Under Credit Agreement			$ 50.0
Credit Agreement [Member] \| Foreign Revolving Loans and Letters of Credit [Member] \| Facility [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 50.0	$ 50.0