Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Contract revenues	$ 125,073	$ 140,162	$ 421,682	$ 416,339
Marine
Disaggregation of Revenue [Line Items]
Contract revenues	63,479		206,967
Marine | Construction
Disaggregation of Revenue [Line Items]
Contract revenues	46,113		141,348
Marine | Dredging
Disaggregation of Revenue [Line Items]
Contract revenues	13,053		53,536
Marine | Specialty Services
Disaggregation of Revenue [Line Items]
Contract revenues	4,313		12,083
Concrete
Disaggregation of Revenue [Line Items]
Contract revenues	61,594		214,715
Concrete | Light Commercial
Disaggregation of Revenue [Line Items]
Contract revenues	48,458		167,140
Concrete | Structural
Disaggregation of Revenue [Line Items]
Contract revenues	13,054		47,166
Concrete | Other
Disaggregation of Revenue [Line Items]
Contract revenues	$ 82		$ 409