Schedule of Senior Unsecured Notes Redemption Prices (Detail) - 4.500% Senior Unsecured Notes Due 2026 [Member]	6 Months Ended
	Sep. 30, 2018
2021 [Member]
Debt Instrument Redemption [Line Items]
Redemption price, percentage	102.25%
2022 [Member]
Debt Instrument Redemption [Line Items]
Redemption price, percentage	101.50%
2023 [Member]
Debt Instrument Redemption [Line Items]
Redemption price, percentage	100.75%
2024 and Thereafter [Member]
Debt Instrument Redemption [Line Items]
Redemption price, percentage	100.00%