Revenue (Summary of Type of Customer, Contract Revenues) (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2022	Mar. 31, 2021
Disaggregation Of Revenue [Line Items]
Revenues	$ 194,349	$ 177,633
Type of Customer [Member] \| Operating Segment [Member] \| Dredging [Member]
Disaggregation Of Revenue [Line Items]
Revenues	194,349	177,633
Type of Customer [Member] \| Operating Segment [Member] \| Dredging [Member] \| Federal Government [Member]
Disaggregation Of Revenue [Line Items]
Revenues	167,574	130,732
Type of Customer [Member] \| Operating Segment [Member] \| Dredging [Member] \| State and Local Government [Member]
Disaggregation Of Revenue [Line Items]
Revenues	24,601	34,775
Type of Customer [Member] \| Operating Segment [Member] \| Dredging [Member] \| Private [Member]
Disaggregation Of Revenue [Line Items]
Revenues	$ 2,174	7,417
Type of Customer [Member] \| Operating Segment [Member] \| Dredging [Member] \| Foreign [Member]
Disaggregation Of Revenue [Line Items]
Revenues		$ 4,709

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
-Paragraph 30
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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+ Details