Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Income Statement [Abstract]
Contract revenues	$ 177,633	$ 217,695
Type of Revenue [Extensible List]	gldd:ContractMember	gldd:ContractMember
Costs of contract revenues	$ 144,557	$ 149,221
Type of Cost, Good or Service [Extensible List]	gldd:ContractMember	gldd:ContractMember
Gross profit	$ 33,076	$ 68,474
General and administrative expenses	16,322	15,571
(Gain) loss on sale of assets—net	106	(145)
Operating income	16,648	53,048
Interest expense—net	(6,586)	(6,630)
Other income (expense)	141	(1,121)
Income before income taxes	10,203	45,297
Income tax provision	(1,389)	(11,310)
Net income	$ 8,814	$ 33,987
Basic earnings per share	$ 0.14	$ 0.53
Basic weighted average shares	65,269	64,455
Diluted earnings per share	$ 0.13	$ 0.52
Diluted weighted average shares	66,159	65,717