Represent the minimum interest coverage ratio under the credit agreement.

No definition available.

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Data Type:	xbrli:decimalItemType
Balance Type:	na
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- 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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Data Type:	xbrli:integerItemType
Balance Type:	na
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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- 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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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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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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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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Balance Type:	na
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- 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
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- 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

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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

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://fasb.org/us-gaap/role/ref/legacyRef
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-SubTopic 10
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+ 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 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

+ 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

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Debt - Narrative (Details) $ in Millions		12 Months Ended
Debt - Narrative (Details) $ in Millions	Jun. 30, 2016 USD ($)	Dec. 31, 2018 USD ($) equipment-note	Sep. 28, 2018 USD ($)	Dec. 31, 2017 USD ($)
Debt Instrument [Line Items]
Debt Instrument Number Of Debt Instruments \| equipment-note		5
Secured Debt [Member] \| Credit Agreement [Member]
Debt Instrument [Line Items]
Option to increase borrowing capacity	$ 100.0
Maximum borrowing capacity	$ 250.0
Interest coverage ratio		3.0
Percentage of Capital Stock From Direct Foreign Subsidiaries	65.00%
Maximum Acquisition Consideration Under Credit Agreement		$ 50.0
Debt Issuance Costs, Line of Credit Arrangements, Net		$ 0.6
Debt Instrument Covenant Leveraged Debt Ratio Restriction		2.25
Leverage Coverage Ratio Expansion		3.5
Leverage Coverage Ratio		3.0
Debt Instrument, Term	5 years
Line of Credit Facility, Interest Rate During Period		3.08%
Secured Debt [Member] \| Credit Agreement [Member] \| Canada, Dollars [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 50.0
Secured Debt [Member] \| Credit Agreement [Member] \| Letter of Credit [Member]
Debt Instrument [Line Items]
Letters of Credit Outstanding, Amount		$ 21.2	$ 150.0	$ 20.9
Secured Debt [Member] \| Credit Agreement [Member] \| Letter of Credit [Member] \| Insurance Program Obligations [Member]
Debt Instrument [Line Items]
Long-term Line of Credit		17.6		17.6
Secured Debt [Member] \| Credit Agreement [Member] \| Letter of Credit [Member] \| Contract Performance Obligations [Member]
Debt Instrument [Line Items]
Long-term Line of Credit		$ 3.6		$ 3.3
Secured Debt [Member] \| Credit Agreement [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage		0.375%
Secured Debt [Member] \| Credit Agreement [Member] \| Maximum [Member] \| Performance letters of credit [Member]
Debt Instrument [Line Items]
Letter of credit facility commitment percentage		1.125%
Secured Debt [Member] \| Credit Agreement [Member] \| Maximum [Member] \| Non-performance Letters Of Credit [Member]
Debt Instrument [Line Items]
Letter of credit facility commitment percentage		2.125%
Secured Debt [Member] \| Credit Agreement [Member] \| Maximum [Member] \| London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Interest rate margin (as a percent)		2.00%
Secured Debt [Member] \| Credit Agreement [Member] \| Maximum [Member] \| Base Rate [Member]
Debt Instrument [Line Items]
Interest rate margin (as a percent)		1.00%
Secured Debt [Member] \| Credit Agreement [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage		0.20%
Secured Debt [Member] \| Credit Agreement [Member] \| Minimum [Member] \| Performance letters of credit [Member]
Debt Instrument [Line Items]
Letter of credit facility commitment percentage		0.625%
Secured Debt [Member] \| Credit Agreement [Member] \| Minimum [Member] \| Non-performance Letters Of Credit [Member]
Debt Instrument [Line Items]
Letter of credit facility commitment percentage		1.125%
Secured Debt [Member] \| Credit Agreement [Member] \| Minimum [Member] \| London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Interest rate margin (as a percent)		1.00%
Secured Debt [Member] \| Credit Agreement [Member] \| Minimum [Member] \| Base Rate [Member]
Debt Instrument [Line Items]
Interest rate margin (as a percent)		0.00%