Senior Notes and Other Long-Term Debt - Components of Long-Term Debt (Parenthetical) (Detail) - Ex-Im Credit Facility [Member] - USD ($) $ in Millions	Sep. 30, 2017	Mar. 31, 2017
Other Long-Term Debt
Exposure fees included in the principal	$ 35.3	$ 29.5
Unamortized discount and debt issuance costs on Ex-Im Credit Facility related to the exposure fees		$ 23.0