Income Taxes - Components of Deferred Tax Assets (Detail) - USD ($) $ in Thousands |
Dec. 31, 2016 |
Dec. 31, 2015 |
|---|---|---|
| Income Tax Disclosure [Abstract] | ||
| Net operating loss carryforwards | $ 44,929 | $ 40,215 |
| Research and development credit carryforwards | 6,017 | 4,454 |
| Compensation expense | 2,735 | 3,300 |
| Other | 1,266 | 1,129 |
| Total deferred tax assets | 54,947 | 49,098 |
| Valuation allowance for deferred tax assets | (54,772) | (48,921) |
| Net deferred tax assets | $ 175 | $ 177 |