Balance Sheet Components - Summary of Accrued Liabilities (Detail) - USD ($) $ in Thousands |
Jun. 30, 2015 |
Dec. 31, 2014 |
|---|---|---|
| Payables and Accruals [Abstract] | ||
| Accrued offering costs | $ 615 | |
| Accrued employee related costs | 572 | $ 759 |
| Accrued research and development costs | 686 | 526 |
| Accrued professional fees | 408 | 140 |
| Other | 23 | 48 |
| Total accrued liabilities | $ 2,304 | $ 1,473 |