Operating Segments - Summarized Segment Financial Information (Parenthetical) (Details) - Forty-Vehicle Ferry $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2019 USD ($) Vechicle	Sep. 30, 2020 Vechicle	Sep. 30, 2019 USD ($) Vechicle
Segment Reporting Information [Line Items]
Revenue reclassified between the Shipyard and Fabrication & Services segments \| $	$ 3.9		$ 7.2
Number of vehicle ferry projects \| Vechicle	2	2	2

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

Name:	us-gaap_SegmentReportingInformationLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration