Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disaggregation of Revenue [Line Items]
Contract revenues	$ 159,767	$ 137,420	$ 296,610	$ 276,177
Marine
Disaggregation of Revenue [Line Items]
Contract revenues	80,698		143,489
Marine | Construction
Disaggregation of Revenue [Line Items]
Contract revenues	52,860		95,235
Marine | Dredging
Disaggregation of Revenue [Line Items]
Contract revenues	23,472		40,483
Marine | Specialty Services
Disaggregation of Revenue [Line Items]
Contract revenues	4,366		7,771
Concrete
Disaggregation of Revenue [Line Items]
Contract revenues	79,069		153,121
Concrete | Light Commercial
Disaggregation of Revenue [Line Items]
Contract revenues	62,189		118,682
Concrete | Structural
Disaggregation of Revenue [Line Items]
Contract revenues	16,740		34,112
Concrete | Other
Disaggregation of Revenue [Line Items]
Contract revenues	$ 140		$ 327