Fair Value of Financial Instruments - Level 3 Roll Forward (Details) $ in Thousands |
3 Months Ended |
|---|---|
|
Mar. 31, 2018
USD ($)
| |
| Series D preferred stock warrants | |
| Fair values of preferred stock warrant liabilities and common stock warrant liability | |
| Beginning Balance | $ 992 |
| Change in fair value | 328 |
| Ending Balance | 1,320 |
| Common stock warrants | |
| Fair values of preferred stock warrant liabilities and common stock warrant liability | |
| Beginning Balance | 1,774 |
| Change in fair value | 2,553 |
| Ending Balance | $ 4,327 |