Revenue (Summary of Type of Customer, Contract Revenues) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 648,781	$ 726,149	$ 733,601
Foreign [Member]
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	149	6,596	25,892
Type of Customer [Member] | Operating Segment [Member] | Dredging [Member]
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	648,781	726,149	733,601
Type of Customer [Member] | Operating Segment [Member] | Dredging [Member] | Federal Government [Member]
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	431,705	568,980	582,949
Type of Customer [Member] | Operating Segment [Member] | Dredging [Member] | State and Local Government [Member]
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	207,033	118,712	85,737
Type of Customer [Member] | Operating Segment [Member] | Dredging [Member] | Private [Member]
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	9,894	31,861	39,023
Type of Customer [Member] | Operating Segment [Member] | Dredging [Member] | Foreign [Member]
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 149	$ 6,596	$ 25,892