Represent the minimum interest coverage ratio under the credit agreement.

No definition available.

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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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Period Type:	duration

- Definition

The number of debt instruments.

+ References

No definition available.

+ Details

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

- Definition

Amount of company's consolidated liquidity restricted.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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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Data Type:	xbrli:decimalItemType
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- 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

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

+ References

No definition available.

+ Details

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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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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

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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

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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 the line of credit facility regardless of whether the facility has been used.

+ References

No definition available.

+ Details

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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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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

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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

- Definition

The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

+ 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 210.5-02.17)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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

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Debt - Additional information (Details) $ in Millions		9 Months Ended
Debt - Additional information (Details) $ in Millions	Sep. 13, 2019 USD ($)	Sep. 30, 2019 USD ($) item	Dec. 31, 2018 USD ($)
Secured Debt [Member] \| Credit Agreement [Member]
Debt Instrument [Line Items]
Debt instrument term	5 years
Maximum borrowing capacity	$ 375.0
Option to increase borrowing capacity	$ 200.0
Percentage of capital stock from direct foreign subsidiaries	65.00%
Debt instrument covenant leveraged debt ratio restriction		2.50
Interest rate on borrowings outstanding		3.46%
Leverage coverage ratio		3.0
Interest coverage ratio		3.0
Debt instrument restricted maximum liquidity		$ 50.0
Deferred debt issuance costs		1.5
Unamortized deferred debt issuance costs		0.4
Secured Debt [Member] \| Credit Agreement [Member] \| Canada, Dollars [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 75.0
Secured Debt [Member] \| Credit Agreement [Member] \| Letter of Credit [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 150.0
Letters of credit outstanding		$ 19.7	$ 21.2
Secured Debt [Member] \| Credit Agreement [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Commitment fee on unused capacity		0.25%
Secured Debt [Member] \| Credit Agreement [Member] \| Maximum [Member] \| Performance letters of credit [Member]
Debt Instrument [Line Items]
Letter of credit facility commitment percentage		0.875%
Secured Debt [Member] \| Credit Agreement [Member] \| Maximum [Member] \| Non-performance Letters Of Credit [Member]
Debt Instrument [Line Items]
Letter of credit facility commitment percentage		1.75%
Secured Debt [Member] \| Credit Agreement [Member] \| Maximum [Member] \| London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Interest rate margin		1.75%
Secured Debt [Member] \| Credit Agreement [Member] \| Maximum [Member] \| Base Rate [Member]
Debt Instrument [Line Items]
Interest rate margin		0.75%
Secured Debt [Member] \| Credit Agreement [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Commitment fee on unused capacity		0.15%
Secured Debt [Member] \| Credit Agreement [Member] \| Minimum [Member] \| Performance letters of credit [Member]
Debt Instrument [Line Items]
Letter of credit facility commitment percentage		0.50%
Secured Debt [Member] \| Credit Agreement [Member] \| Minimum [Member] \| Non-performance Letters Of Credit [Member]
Debt Instrument [Line Items]
Letter of credit facility commitment percentage		1.00%
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%
Secured Debt [Member] \| Insurance Program Obligations [Member] \| Credit Agreement [Member] \| Letter of Credit [Member]
Debt Instrument [Line Items]
Letters of credit outstanding		$ 18.5	17.6
Secured Debt [Member] \| Contract Performance Obligations [Member] \| Credit Agreement [Member] \| Letter of Credit [Member]
Debt Instrument [Line Items]
Letters of credit outstanding		$ 1.2	$ 3.6
Notes Payable to Banks [Member] \| Master Loan Agreement [Member]
Debt Instrument [Line Items]
Number of equipment notes (equipment note) \| item		7