Income Taxes - Deferred Tax Assets (Detail) - USD ($) $ in Thousands |
Dec. 31, 2015 |
Dec. 31, 2014 |
|---|---|---|
| Deferred tax assets: | ||
| Net operating loss carryforwards | $ 37,017 | $ 41,846 |
| Capitalized research and development costs | 2,431 | 2,646 |
| Research and development credit carryforwards | 3,510 | 2,360 |
| Stock compensation | 5,369 | 2,479 |
| Depreciation and other costs | 372 | |
| Depreciation and other costs | (74) | |
| Net deferred tax assets | 48,253 | 49,703 |
| Valuation allowance | (48,253) | (49,703) |
| Net deferred tax assets | $ 0 | $ 0 |