Revenue (Summary of Type of Customer, Contract Revenues) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 117,185	$ 158,346	$ 407,896	$ 502,123
Type of Customer [Member] | Operating Segment [Member] | Dredging [Member]
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	117,185	158,346	407,896	502,123
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	78,681	62,228	328,211	325,162
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	33,316	91,544	74,497	167,067
Type of Customer [Member] | Operating Segment [Member] | Dredging [Member] | Private [Member]
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 5,188	$ 4,574	$ 5,188	$ 9,894