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Revenue (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024	Dec. 31, 2024
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue, remaining performance obligation on dredging contracts	$ 934.5		$ 934.5
Remaining performance obligations exclude from dredging backlog	73.0		73.0
Performance obligations domestic low bids pending formal award and additional phases	193.5		193.5
Amortization on pre-construction costs	2.8	$ 4.4	12.0	$ 12.8
Other Current Assets [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Costs to fulfill contract customers recognized as asset	12.8		12.8		$ 10.3
Other Noncurrent Assets [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Costs to fulfill contract customers recognized as asset	$ 1.6		$ 1.6		$ 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

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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