Revenue (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Revenue From Contract With Customer [Line Items]
Revenue, remaining performance obligation	$ 551,588
Percentage of performance obligation to be recognized as revenue	88.00%
Performance obligation, expected to be recognized as revenue year	2022
Remaining performance obligation, expected timing of satisfaction, year	2023
Amortization on pre-contract and pre-construction costs	$ 17,839	$ 15,541
Contract revenues	726,149	733,601	$ 711,518
Long-lived assets, net book value	0	5,225
Dredging [Member] \| Use of Equipment [Member] \| Federal Government [Member]
Revenue From Contract With Customer [Line Items]
Contract revenues	$ 716	$ 616
Dredging [Member] \| Sales [Member] \| Geographic Concentration Risk [Member] \| Middle East [Member] \| Maximum [Member]
Revenue From Contract With Customer [Line Items]
Concentration risk percentage	10.00%	10.00%	10.00%
Dredging [Member] \| Sales [Member] \| Federal Government Agencies [Member] \| Customer Concentration Risk [Member]
Revenue From Contract With Customer [Line Items]
Concentration risk percentage	78.40%	79.50%	81.70%
Dredging [Member] \| Accounts Receivable [Member] \| Geographic Concentration Risk [Member] \| Middle East [Member]
Revenue From Contract With Customer [Line Items]
Concentration risk percentage	9.00%	12.00%
Dredging [Member] \| Accounts Receivable [Member] \| Federal Government Agencies [Member] \| Customer Concentration Risk [Member]
Revenue From Contract With Customer [Line Items]
Concentration risk percentage	68.50%	42.60%
Other Current and Noncurrent Assets [Member]
Revenue From Contract With Customer [Line Items]
Costs to fulfill contracts with customers recognized as an asset	$ 5,652	$ 10,501

Percentage of performance obligation to be recognized as revenue.

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Performance obligation expected to be recognized as revenue, year.

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Revenue from contract with customer line items.

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Amount of accumulated amortization of asset recognized from cost incurred to obtain or fulfill contract with customer.

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Amount, before accumulated amortization and accumulated impairment loss, of asset recognized from cost incurred to obtain or fulfill contract with customer.

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Long-lived assets other than financial instruments, long-term customer relationships of a financial institution, mortgage and other servicing rights, deferred policy acquisition costs, and deferred tax assets.

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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.

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Amount of transaction price allocated to performance obligation that has not been recognized as revenue.

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Year in which remaining performance obligation is expected to be recognized, in YYYY format.

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