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Revenue (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024	Dec. 31, 2024
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue, remaining performance obligation on dredging contracts	$ 960.4		$ 960.4
Remaining performance obligations exclude from dredging backlog	52.4		52.4
Performance obligations domestic low bids pending formal award and additional phases	$ 215.4		$ 215.4
Percentage of performance obligation to be recognized as revenue			40.00%
Performance obligation, expected to be recognized as revenue year			2025
Remaining performance obligation, expected timing of satisfaction, year	2025 2026		2025 2026
Amortization on pre-construction costs	$ 5.8	$ 4.0	$ 9.2	$ 8.4
Contracts and options pending award related to offshore wind contracts	14.5		14.5
Other Current Assets [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Costs to fulfill contract customers recognized as asset	8.3		8.3		$ 10.3
Other Noncurrent Assets [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Costs to fulfill contract customers recognized as asset	$ 1.9		$ 1.9		$ 7.6

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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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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 340
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-Section 50
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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-SubTopic 10
-Topic 606
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