Income Taxes - Significant Components of Net Deferred Tax Assets (Detail) - USD ($) $ in Thousands |
Dec. 31, 2016 |
Dec. 31, 2015 |
|---|---|---|
| Income Tax Disclosure [Abstract] | ||
| Net operating loss carry forwards | $ 32,500 | $ 33,684 |
| Research and development tax credits | 8,142 | 4,982 |
| Stock based compensation and other | 7,256 | 4,465 |
| Depreciation and amortization | 78 | 42 |
| Total deferred tax assets | 47,976 | 43,173 |
| Less: Valuation allowance | $ (47,976) | $ (43,173) |