Fair Value Measurements - Level 3 Instruments Reconciliation (Details) - Warrants - Recurring basis - Significant Other Unobservable Inputs (Level 3) - USD ($) $ in Thousands |
12 Months Ended | |
|---|---|---|
Dec. 31, 2016 |
Dec. 31, 2015 |
|
| Reconciliations of the beginning and ending balances for liabilities measured at fair value on a recurring basis using significant unobservable inputs (i.e. Level 3) | ||
| Balance at the beginning of the period | $ 5,735 | $ 9,418 |
| Change in fair value of common stock warrants | (4,344) | (3,661) |
| Issuance of common stock warrants | 10,137 | |
| Exercise of common stock warrants | (141) | (22) |
| Balance at the end of the period | $ 11,387 | $ 5,735 |