Percentage of performance obligation to be recognized as revenue.

No definition available.

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Namespace Prefix:	gldd_
Data Type:	num:percentItemType
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Period Type:	duration

- Definition

Performance obligation expected to be recognized as revenue, year.

+ References

No definition available.

+ Details

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Namespace Prefix:	gldd_
Data Type:	xbrli:gYearItemType
Balance Type:	na
Period Type:	duration

- Definition

Revenue from contract with customer line items.

+ References

No definition available.

+ Details

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Namespace Prefix:	gldd_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of amortization expense for asset recognized from cost incurred to obtain or fulfill contract with customer.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 340
-SubTopic 40
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=68051541&loc=SL49131252-203054

+ Details

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

- Definition

Amount, before accumulated amortization and accumulated impairment loss, of asset recognized from cost incurred to obtain or fulfill contract with customer.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 340
-SubTopic 40
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=68051541&loc=SL49131252-203054

+ Details

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

- Definition

Amount of transaction price allocated to performance obligation that has not been recognized as revenue.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130556-203045

+ Details

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

- Definition

Year in which remaining performance obligation is expected to be recognized, in CCYY format.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130556-203045

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	us-types:gYearListItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_BalanceSheetLocationAxis=gldd_OtherCurrentAndNoncurrentAssetsMember
Namespace Prefix:
Data Type:	na
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Period Type:

Revenue (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
Revenue (Narrative) (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Revenue From Contract With Customer [Line Items]
Revenue, remaining performance obligation	$ 454,402		$ 454,402
Percentage of performance obligation to be recognized as revenue			93.00%
Performance obligation, expected to be recognized as revenue year			2021
Remaining performance obligation, expected timing of satisfaction, year	2022		2022
Amortization on pre-construction costs	$ 5,909	$ 3,612	$ 11,756	$ 8,804
Other Current and Noncurrent Assets [Member]
Revenue From Contract With Customer [Line Items]
Costs to fulfill a contract with customer recognized as an asset	$ 6,887		$ 6,887		$ 10,501