Income Taxes - Changes in Valuation Allowance for Deferred Tax Assets (Detail) - USD ($) $ in Thousands |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2015 |
Dec. 31, 2014 |
Dec. 31, 2013 |
|
| Income Tax Disclosure [Abstract] | |||
| Valuation allowance as of beginning of year | $ 36,825 | $ 25,776 | $ 19,815 |
| Decreases recorded as benefit to income tax provision | 0 | 0 | 0 |
| Increases recorded to income tax provision | 15,144 | 11,049 | 5,961 |
| Valuation allowance as of end of year | $ 51,969 | $ 36,825 | $ 25,776 |