Senior Notes and Other Long-Term Debt - Components of Long-Term Debt (Detail) - USD ($)	Sep. 30, 2020	Mar. 31, 2020
Debt Instrument [Line Items]
Finance lease obligations (see Note 6)	$ 62,872,000	$ 64,956,000
Total debt	1,870,959,000	1,872,869,000
Unamortized discount and debt issuance costs	(23,981,000)	(21,418,000)
Less: current portion of long-term debt	32,301,000	29,788,000
Total long-term debt	1,814,677,000	1,821,663,000
2028 Notes [Member]
Debt Instrument [Line Items]
Principal amount of debt	400,000,000
2027 Notes [Member]
Debt Instrument [Line Items]
Principal amount of debt	600,000,000	600,000,000
2025 Notes [Member]
Debt Instrument [Line Items]
Principal amount of debt	700,000,000	700,000,000
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Principal amount of debt		390,000,000
Ex-Im Credit Facility [Member]
Debt Instrument [Line Items]
Principal amount of debt	$ 108,087,000	$ 117,913,000

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Present value of lessee's discounted obligation for lease payments from finance lease.

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