Fair Value of Senior Notes (Parenthetical) (Detail) - 4.5% Senior Unsecured Notes Due 2026 [Member] |
6 Months Ended |
|---|---|
Sep. 30, 2016 | |
| Fair Value Of Financial Instruments [Line Items] | |
| Debt instrument, interest rate | 4.50% |
| Debt instrument, maturity year | 2026 |