Revenue (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2020 USD ($) segment	Dec. 31, 2019 USD ($) segment	Dec. 31, 2018 USD ($) segment
Disaggregation of Revenue [Line Items]
Contract revenues	$ 170,176	$ 189,433	$ 183,713	$ 166,620	$ 199,793	$ 199,507	$ 165,985	$ 143,105	$ 709,942	$ 708,390	$ 520,894
Number of reportable segments | segment									2	2	2
Heavy Civil Marine Construction Segment
Disaggregation of Revenue [Line Items]
Contract revenues									$ 388,173	$ 369,138	$ 243,883
Heavy Civil Marine Construction Segment | Construction
Disaggregation of Revenue [Line Items]
Contract revenues									272,870	242,527	156,925
Heavy Civil Marine Construction Segment | Dredging
Disaggregation of Revenue [Line Items]
Contract revenues									106,647	112,303	73,237
Heavy Civil Marine Construction Segment | Specialty Services
Disaggregation of Revenue [Line Items]
Contract revenues									8,656	14,308	13,721
Commercial Concrete Segment
Disaggregation of Revenue [Line Items]
Contract revenues									321,769	339,252	277,011
Commercial Concrete Segment | Structural
Disaggregation of Revenue [Line Items]
Contract revenues									85,904	54,497	60,926
Commercial Concrete Segment | Light Commercial
Disaggregation of Revenue [Line Items]
Contract revenues									235,835	284,624	215,628
Commercial Concrete Segment | Other
Disaggregation of Revenue [Line Items]
Contract revenues									$ 30	$ 131	$ 457