Fair Value Measurements - Schedule of Roll-Forward of Company's Liabilities Measured at Fair Value on Recurring Basis Using Unobservable Inputs (Level 3) (Detail) - USD ($) $ in Thousands |
12 Months Ended | |
|---|---|---|
Dec. 31, 2014 |
Dec. 31, 2013 |
|
| Debt Instrument Fair Value Carrying Value [Abstract] | ||
| Balance at the beginning of the period | $ 529 | $ 331 |
| Issuance of preferred stock warrants | 324 | |
| Change in fair value of warrant liability | (2,559) | (126) |
| Transfers to Level 2 | $ (3,088) | |
| Balance at the end of the period | $ 529 | |