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Summary of Debt Outstanding (Parenthetical) (Detail) - Level 2 - USD ($) $ in Millions	Sep. 30, 2017	Mar. 31, 2017
Term loan, revolving line of credit and senior notes
Debt [Line Items]
Fair value of debt		$ 1,100.0
New Secured Notes
Debt [Line Items]
Fair value of debt	$ 357.7
Troms Offshore borrowings
Debt [Line Items]
Fair value of debt	$ 90.9	$ 92.9

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