Available-for-Sale Securities - Summary of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands |
Sep. 30, 2016 |
Dec. 31, 2015 |
|---|---|---|
| Schedule Of Available For Sale Securities [Line Items] | ||
| Amortized Cost | $ 75,024 | |
| Aggregate Fair Value | 75,054 | |
| U.S. Treasury Securities | ||
| Schedule Of Available For Sale Securities [Line Items] | ||
| Amortized Cost | 75,024 | $ 250,215 |
| Gross Unrealized Gains | 30 | |
| Gross Unrealized Losses | (383) | |
| Aggregate Fair Value | $ 75,054 | $ 249,832 |