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v3.21.1

Subsequent Event (Details) $ in Millions | Apr. 13, 2021 USD ($)
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Equipment Note 7 | Subsequent Event |
Subsequent Event [Line Items] |
Prepayment of equipment note | $ 7.0

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- Definition Amount of cash inflow (outflow) from long-term debt supported by a written promise to pay an obligation. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 3 -Subparagraph (SX 210.12-04(a)) -URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e24072-122690 + Details
Name: | us-gaap_ProceedsFromRepaymentsOfNotesPayable
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event. + References No definition available. + Details
Name: | us-gaap_SubsequentEventLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_DebtInstrumentAxis=myrg_EquipmentNoteSevenMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |