Revenue (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($) segment	Mar. 31, 2019 USD ($)
Disaggregation of Revenue [Line Items]
Contract revenues	$ 166,620	$ 143,105
Number of reportable segments | segment	2
Marine
Disaggregation of Revenue [Line Items]
Contract revenues	$ 85,949	61,487
Marine | Construction
Disaggregation of Revenue [Line Items]
Contract revenues	53,140	33,636
Marine | Dredging
Disaggregation of Revenue [Line Items]
Contract revenues	30,899	26,167
Marine | Specialty Services
Disaggregation of Revenue [Line Items]
Contract revenues	1,910	1,684
Concrete
Disaggregation of Revenue [Line Items]
Contract revenues	80,671	81,618
Concrete | Structural
Disaggregation of Revenue [Line Items]
Contract revenues	21,236	11,491
Concrete | Light Commercial
Disaggregation of Revenue [Line Items]
Contract revenues	59,433	70,096
Concrete | Other
Disaggregation of Revenue [Line Items]
Contract revenues	$ 2	$ 31