Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Income Statement [Abstract]
Contract revenues	$ 217,695	$ 192,637
Type of Revenue [Extensible List]	gldd:ContractMember	gldd:ContractMember
Costs of contract revenues	$ 149,221	$ 142,760
Type of Cost, Good or Service [Extensible List]	gldd:ContractMember	gldd:ContractMember
Gross profit	$ 68,474	$ 49,877
General and administrative expenses	15,571	14,825
(Gain) loss on sale of assets—net	(145)	279
Operating income	53,048	34,773
Interest expense—net	(6,630)	(7,551)
Other income (expense)	(1,121)	172
Income from continuing operations before income taxes	45,297	27,394
Income tax provision	(11,310)	(6,846)
Income from continuing operations	33,987	20,548
Loss from discontinued operations, net of income taxes		(3,380)
Net income	$ 33,987	$ 17,168
Basic earnings per share attributable to continuing operations	$ 0.53	$ 0.33
Basic loss per share attributable to discontinued operations, net of tax		(0.05)
Basic earnings per share	$ 0.53	$ 0.28
Basic weighted average shares	64,455	62,882
Diluted earnings per share attributable to continuing operations	$ 0.52	$ 0.32
Diluted loss per share attributable to discontinued operations, net of tax		(0.05)
Diluted earnings per share	$ 0.52	$ 0.27
Diluted weighted average shares	65,717	64,569