Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Income Statement [Abstract]
Contract revenues	$ 169,914	$ 167,920	$ 347,547	$ 385,615
Type of Revenue [Extensible List]	gldd:ContractMember	gldd:ContractMember	gldd:ContractMember	gldd:ContractMember
Costs of contract revenues	$ 146,992	$ 134,904	$ 291,549	$ 284,125
Type of Cost, Good or Service [Extensible List]	gldd:ContractMember	gldd:ContractMember	gldd:ContractMember	gldd:ContractMember
Gross profit	$ 22,922	$ 33,016	$ 55,998	$ 101,490
General and administrative expenses	14,224	14,804	30,546	30,375
Gain on sale of assets—net	(138)	(39)	(32)	(184)
Operating income	8,836	18,251	25,484	71,299
Interest expense—net	(6,657)	(6,725)	(13,243)	(13,355)
Other income (expense)	755	565	896	(556)
Income before income taxes	2,934	12,091	13,137	57,388
Income tax provision	(829)	(3,131)	(2,218)	(14,441)
Net income	$ 2,105	$ 8,960	$ 10,919	$ 42,947
Basic earnings per share	$ 0.03	$ 0.14	$ 0.17	$ 0.66
Basic weighted average shares	65,646	64,864	65,458	64,659
Diluted earnings per share	$ 0.03	$ 0.14	$ 0.16	$ 0.65
Diluted weighted average shares	66,137	65,758	66,187	65,802