Commitments and Contingencies - Narrative (Details) $ in Millions	Sep. 30, 2018 USD ($) vessel	Mar. 31, 2018 USD ($) vessel
Loss Contingencies [Line Items]
Number of multi-purpose service vessels	2
Balance sheet exposure \| $	$ 12.5
U.S. Navy [Member]
Loss Contingencies [Line Items]
Number of towing, salvage and rescue vessels		1
Construction in progress \| $		$ 63.6
Number of additional vessels		7

Construction In Progress, Number Of Additional Vessels1

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Construction In Progress, Number Of Multi-Purpose Service Vessels

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Construction In Progress, Number Of Towing, Salvage, And Rescue Ship Vessels

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Amount of structure or a modification to a structure under construction. Includes recently completed structures or modifications to structures that have not been placed into service.

+ References

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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.

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Reflects the estimated amount of loss from the specified contingency as of the balance sheet date.

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