Fair Value of Financial Assets and Liabilities - Schedule of Aggregate Fair Values of Preferred Stock Warrants Determined by Level 3 Inputs (Detail) - USD ($) $ in Thousands |
12 Months Ended | |
|---|---|---|
Dec. 31, 2014 |
Dec. 31, 2013 |
|
| Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] | ||
| Beginning Balance | $ 254 | $ 268 |
| Increase/Decrease in fair value | 380 | (14) |
| Conversion of preferred stock warrants to common stock warrants (Note 8) | (960) | |
| Ending Balance | $ 254 | |
| Series D-1 Warrants [Member] | ||
| Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] | ||
| Issuance of warrants | $ 326 | |