Investments - Investments in Continuous Unrealized Loss Position for Less Than Twelve Months (Detail) - USD ($) $ in Thousands |
Jun. 30, 2016 |
Dec. 31, 2015 |
|---|---|---|
| Schedule of Available-for-sale Securities [Line Items] | ||
| Fair Value | $ 102,983 | $ 247,297 |
| Unrealized Losses | (49) | (828) |
| Commercial Paper [Member] | ||
| Schedule of Available-for-sale Securities [Line Items] | ||
| Fair Value | 12,394 | 5,981 |
| Unrealized Losses | (15) | (5) |
| US Government Agencies [Member] | ||
| Schedule of Available-for-sale Securities [Line Items] | ||
| Fair Value | 5,505 | 8,969 |
| Unrealized Losses | (1) | (30) |
| Corporate Bonds and Notes [Member] | ||
| Schedule of Available-for-sale Securities [Line Items] | ||
| Fair Value | 85,084 | 232,347 |
| Unrealized Losses | $ (33) | $ (793) |