Fair Value Measurements - Narrative (Detail) - USD ($) |
Apr. 30, 2017 |
Jan. 31, 2017 |
Jun. 30, 2013 |
|---|---|---|---|
| Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | |||
| Closing price of company's common stock, dollars per share | $ 87.4 | ||
| 2018 Notes | |||
| Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | |||
| Convertible senior notes, principal amount | $ 350,000,000 | $ 350,000,000 | $ 350,000,000 |
| Contractual interest rate | 0.75% | 0.75% | |
| 2020 Notes | |||
| Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | |||
| Convertible senior notes, principal amount | $ 250,000,000 | $ 250,000,000 | $ 250,000,000 |
| Contractual interest rate | 1.50% | 1.50% |