Revenue (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2021 USD ($) segment	Mar. 31, 2020 USD ($) segment
Disaggregation of Revenue [Line Items]
Contract revenues	$ 153,309	$ 166,620
Number of reportable segments | segment	2	2
Heavy Civil Marine Construction Segment
Disaggregation of Revenue [Line Items]
Contract revenues	$ 72,146	$ 85,949
Heavy Civil Marine Construction Segment | Construction
Disaggregation of Revenue [Line Items]
Contract revenues	43,936	53,140
Heavy Civil Marine Construction Segment | Dredging
Disaggregation of Revenue [Line Items]
Contract revenues	24,682	30,899
Heavy Civil Marine Construction Segment | Specialty Services
Disaggregation of Revenue [Line Items]
Contract revenues	3,528	1,910
Commercial Concrete Segment
Disaggregation of Revenue [Line Items]
Contract revenues	81,163	80,671
Commercial Concrete Segment | Structural
Disaggregation of Revenue [Line Items]
Contract revenues	16,661	21,236
Commercial Concrete Segment | Light Commercial
Disaggregation of Revenue [Line Items]
Contract revenues	64,495	59,433
Commercial Concrete Segment | Other
Disaggregation of Revenue [Line Items]
Contract revenues	$ 7	$ 2