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Employee Benefit Plans - Additional information (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($) item	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Multiemployer Plans, Pension [Member]
Number of local unions (union) | item	100
Other Postretirement Benefits Plan [Member] | UNITED STATES [Member] | Profit Sharing And Thrift Employee Benefit Plan [Member]
Contributions to benefit plans | $	$ 10.9	$ 5.8	$ 4.1

X

- Definition

Represents the number of local unions.

+ References

No definition available.

+ Details

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

X

- Definition

Amount of cost for defined contribution plan.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 70
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942

+ Details

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Balance Type:	debit
Period Type:	duration

X

- Details

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Namespace Prefix:
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Balance Type:
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X

- Details

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Namespace Prefix:
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X

- Details

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Namespace Prefix:
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X

- Details

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