Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disaggregation of Revenue [Line Items]
Contract revenues	$ 165,985	$ 159,767	$ 309,090	$ 296,610
Marine
Disaggregation of Revenue [Line Items]
Contract revenues	89,023	80,698	150,510	143,489
Marine | Construction
Disaggregation of Revenue [Line Items]
Contract revenues	57,181	52,860	90,817	95,235
Marine | Dredging
Disaggregation of Revenue [Line Items]
Contract revenues	27,191	23,472	53,358	40,483
Marine | Specialty Services
Disaggregation of Revenue [Line Items]
Contract revenues	4,651	4,366	6,335	7,771
Concrete
Disaggregation of Revenue [Line Items]
Contract revenues	76,962	79,069	158,580	153,121
Concrete | Structural
Disaggregation of Revenue [Line Items]
Contract revenues	12,665	62,189	24,156	118,682
Concrete | Light Commercial
Disaggregation of Revenue [Line Items]
Contract revenues	64,275	16,740	134,371	34,112
Concrete | Other
Disaggregation of Revenue [Line Items]
Contract revenues	$ 22	$ 140	$ 53	$ 327