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Revenue (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Revenue From Contract With Customer [Line Items]
Revenue, remaining performance obligation	$ 807.9		$ 807.9
Performance obligations exclude from dredging backlog	44.6		44.6
Performance obligations domestic low bids pending formal award and additional phases	$ 273.1		$ 273.1
Percentage of performance obligation to be recognized as revenue			40.00%
Performance obligation, expected to be recognized as revenue year			2024
Remaining performance obligation, expected timing of satisfaction, year	2025 2026		2025 2026
Amortization on pre-construction costs	$ 4.0	$ 1.3	$ 8.4	$ 5.0
Options pending award related to offshore wind contracts	12.7		12.7
Other Current and Noncurrent Assets [Member]
Revenue From Contract With Customer [Line Items]
Costs to fulfill a contract with customer recognized as an asset	$ 21.8		$ 21.8		$ 22.2

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Performance obligation expected to be recognized as revenue, year.

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 340
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479483/340-40-50-3

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+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 340
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479483/340-40-50-3

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (a)
-SubTopic 10
-Topic 606
-Publisher FASB
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Year in which remaining performance obligation is expected to be recognized, in YYYY format.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (b)(1)
-SubTopic 10
-Topic 606
-Publisher FASB
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