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

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

+ References

No definition available.

+ Details

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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 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

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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

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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

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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

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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

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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://www.xbrl.org/2003/role/presentationRef
-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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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

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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

- 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

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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

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

- Details

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Balance Type:
Period Type:

- Details

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Data Type:	na
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- Details

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Data Type:	na
Balance Type:
Period Type:

- Details

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Data Type:	na
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Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=myrg_NonperformanceLettersOfCreditMember
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Period Type:

- Details

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- Details

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- Details

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Data Type:	na
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- Details

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- Details

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Data Type:	na
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- Details

Name:	us-gaap_DebtInstrumentAxis=myrg_ForeignRevolvingLoansAndLettersOfCreditMember
Namespace Prefix:
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Debt (Details Textual) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Debt (Details Textual) - USD ($) $ in Millions	Mar. 31, 2018	Jun. 30, 2016	Dec. 31, 2017
Debt Instrument [Line Items]
Letters of Credit Outstanding, Amount	$ 20.6		$ 20.9
Long-term Line of Credit	67.4		79.0
Debt Issuance Costs, Line of Credit Arrangements, Net	$ 0.7
Debt Instrument Covenant Leveraged Debt Ratio Restriction	2.25
Insurance Programe 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	$ 3.0		$ 3.3
Maximum [Member]
Debt Instrument [Line Items]
Leverage Coverage Ratio Expansion	3.5
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
Credit Agreement [Member]
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	2.75%
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