Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Statement [Abstract]
Contract revenues	$ 184,811	$ 135,270	$ 377,448	$ 268,893
Type of Revenue [Extensible List]	gldd:ContractMember	gldd:ContractMember	gldd:ContractMember	gldd:ContractMember
Costs of contract revenues	$ 147,325	$ 113,138	$ 290,085	$ 232,631
Type of Cost, Good or Service [Extensible List]	gldd:ContractMember	gldd:ContractMember	gldd:ContractMember	gldd:ContractMember
Gross profit	$ 37,486	$ 22,132	$ 87,363	$ 36,262
General and administrative expenses	14,613	12,232	29,438	25,325
(Gain) loss on sale of assets—net	81	(1,057)	360	(1,256)
Operating income	22,792	10,957	57,565	12,193
Interest expense—net	(7,188)	(8,991)	(14,739)	(17,644)
Other income (expense)	123	33	295	(2,032)
Income (loss) from continuing operations before income taxes	15,727	1,999	43,121	(7,483)
Income tax (provision) benefit	(4,230)	(818)	(11,076)	1,657
Income (loss) from continuing operations	11,497	1,181	32,045	(5,826)
Loss from discontinued operations, net of income taxes	(3,251)	(2,155)	(6,631)	(4,469)
Net income (loss)	$ 8,246	$ (974)	$ 25,414	$ (10,295)
Basic earnings (loss) per share attributable to continuing operations	$ 0.18	$ 0.02	$ 0.51	$ (0.09)
Basic loss per share attributable to discontinued operations, net of tax	(0.05)	(0.04)	(0.10)	(0.08)
Basic earnings (loss) per share	$ 0.13	$ (0.02)	$ 0.41	$ (0.17)
Basic weighted average shares	63,605	62,267	63,243	62,041
Diluted earnings (loss) per share attributable to continuing operations	$ 0.18	$ 0.02	$ 0.50	$ (0.09)
Diluted loss per share attributable to discontinued operations, net of tax	(0.05)	(0.04)	(0.10)	(0.08)
Diluted earnings (loss) per share	$ 0.13	$ (0.02)	$ 0.40	$ (0.17)
Diluted weighted average shares	64,990	62,267	64,654	62,041