Fair Value Measurements (Details 3) - USD ($) $ in Thousands |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2015 |
Sep. 30, 2014 |
Sep. 30, 2015 |
Sep. 30, 2014 |
|
| 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 | $ 6,982 | $ 16,129 | $ 9,418 | $ 28,830 |
| Change in fair value of common stock warrants | (2,167) | (485) | (4,603) | 58,371 |
| Issuance of common stock warrants | 11,773 | |||
| Exercise of common stock warrants | (22) | (115) | (22) | (83,445) |
| Balance at the end of the period | $ 4,793 | $ 15,529 | $ 4,793 | $ 15,529 |