Fair Value of Financial Instruments - Rollforward of Level 3 Liabilities (Details) - Significant Unobservable Inputs (Level 3) - Warrant Liability - USD ($) $ in Thousands |
6 Months Ended | |
---|---|---|
Jun. 30, 2018 |
Jun. 30, 2017 |
|
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] | ||
Beginning balance | $ 7,472 | $ 3,367 |
Change in fair value of warrant liability included in earnings | (529) | 177 |
Issuance of common stock on warrant exercise | (552) | 0 |
Ending balance | $ 6,391 | $ 3,544 |