Revenue (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020 USD ($) segment	Jun. 30, 2019 USD ($) segment	Jun. 30, 2020 USD ($) segment	Jun. 30, 2019 USD ($) segment
Disaggregation of Revenue [Line Items]
Contract revenues	$ 183,713	$ 165,985	$ 350,333	$ 309,090
Number of reportable segments | segment	2	2	2	2
Heavy Civil Marine Construction Segment
Disaggregation of Revenue [Line Items]
Contract revenues	$ 91,719	$ 89,023	$ 177,668	$ 150,510
Heavy Civil Marine Construction Segment | Construction
Disaggregation of Revenue [Line Items]
Contract revenues	65,814	57,181	118,954	90,817
Heavy Civil Marine Construction Segment | Dredging
Disaggregation of Revenue [Line Items]
Contract revenues	24,230	27,191	55,129	53,358
Heavy Civil Marine Construction Segment | Specialty Services
Disaggregation of Revenue [Line Items]
Contract revenues	1,675	4,651	3,585	6,335
Commercial Concrete Segment
Disaggregation of Revenue [Line Items]
Contract revenues	91,994	76,962	172,665	158,580
Commercial Concrete Segment | Structural
Disaggregation of Revenue [Line Items]
Contract revenues	24,541	12,665	45,777	24,156
Commercial Concrete Segment | Light Commercial
Disaggregation of Revenue [Line Items]
Contract revenues	67,442	64,275	126,875	134,371
Commercial Concrete Segment | Other
Disaggregation of Revenue [Line Items]
Contract revenues	$ 11	$ 22	$ 13	$ 53