Indebtedness - Carrying Value of Convertible Notes (Parenthetical) (Detail) - Convertible Senior Notes [Member] - 4.25% Convertible Notes [Member] |
3 Months Ended |
|---|---|
Apr. 30, 2016 | |
| Schedule Of Convertible Notes [Line Items] | |
| Remaining period over which unamortized debt discount will be amortized | 30 months |
| Percentage of effective interest rate | 9.00% |