Income Taxes - Components of Net Deferred Tax Assets (Detail) - USD ($) $ in Thousands |
Dec. 31, 2015 |
Dec. 31, 2014 |
|---|---|---|
| Income Tax Disclosure [Abstract] | ||
| Net operating loss carryforwards | $ 13,552 | $ 9,805 |
| Tax credit carryforwards | 442 | 261 |
| Stock-based compensation | 1,744 | 1,392 |
| Licensing deduction deferral | 5,979 | 6,367 |
| Other timing differences | 178 | 110 |
| Gross deferred tax assets | 21,895 | 17,935 |
| Valuation allowance | (21,895) | (17,935) |
| Net deferred tax asset | $ 0 | $ 0 |