Revenue (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($) segment	Sep. 30, 2019 USD ($) segment	Sep. 30, 2020 USD ($) segment	Sep. 30, 2019 USD ($) segment
Disaggregation of Revenue [Line Items]
Contract revenues	$ 189,433	$ 199,507	$ 539,766	$ 508,597
Number of reportable segments | segment	2	2	2	2
Heavy Civil Marine Construction Segment
Disaggregation of Revenue [Line Items]
Contract revenues	$ 112,881	$ 107,404	$ 290,549	$ 257,914
Heavy Civil Marine Construction Segment | Construction
Disaggregation of Revenue [Line Items]
Contract revenues	86,505	72,609	205,459	163,426
Heavy Civil Marine Construction Segment | Dredging
Disaggregation of Revenue [Line Items]
Contract revenues	24,262	29,404	79,391	82,762
Heavy Civil Marine Construction Segment | Specialty Services
Disaggregation of Revenue [Line Items]
Contract revenues	2,114	5,391	5,699	11,726
Commercial Concrete Segment
Disaggregation of Revenue [Line Items]
Contract revenues	76,552	92,103	249,217	250,683
Commercial Concrete Segment | Structural
Disaggregation of Revenue [Line Items]
Contract revenues	21,116	13,439	66,893	37,595
Commercial Concrete Segment | Light Commercial
Disaggregation of Revenue [Line Items]
Contract revenues	$ 55,436	78,587	182,311	212,958
Commercial Concrete Segment | Other
Disaggregation of Revenue [Line Items]
Contract revenues		$ 77	$ 13	$ 130