Senior Notes and Other Long-Term Debt - Components of Long-Term Debt (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Mar. 31, 2016
Senior Notes
Total senior notes long-term, net	$ 575,352	$ 575,304
Other Long-Term Debt
Other	576	562
Total other long-term debt, net	485,405	370,498
Total other long-term debt, net	485,405	370,498
Less: current portion of other long-term debt, net	281	274
Other long-term debt, net	485,124	370,224
Total debt, net	1,060,757	945,802
Less: current portion	281	274
Long-term debt, net	1,060,476	945,528
Revolving Credit Facility [Member]
Other Long-Term Debt
Credit Facility	225,000	180,000
Ex-Im Credit Facility [Member]
Other Long-Term Debt
Credit Facility	264,400
Credit Facility	292,777	218,157
Unamortized discount and debt issuance costs on the Ex-Im Credit Facility	(32,948)	(28,221)
2020 Notes [Member]
Senior Notes
Principal amounts of Senior Notes issued	575,000	575,000
Unamortized premium and debt issuance costs on the 2020 Notes, net	352	304
Total senior notes, net	575,352	575,304
Total senior notes, net	575,352	575,304
Less: current portion of the senior notes	0	0
Total senior notes long-term, net	$ 575,352	$ 575,304