Stock-Based Compensation - Granted to non-employees, prior to the adoption of ASU 2018-07 (Details) - Non-employees - $ / shares |
12 Months Ended | |||
|---|---|---|---|---|
Jan. 01, 2018 |
Dec. 31, 2019 |
Dec. 31, 2018 |
Dec. 31, 2017 |
|
| Fair value of stock awards granted prior to the adoption of ASU 2018-07 | ||||
| Risk-free interest rate | 2.30% | 2.07% | 2.71% | 2.05% |
| Expected volatility | 74.00% | 76.90% | 74.00% | 75.60% |
| Expected term (in years) | 6 years 1 month 6 days | 6 years 22 days | 6 years 2 months 16 days | 6 years 4 months 21 days |
| ASU 2018-07 | Minimum | ||||
| Fair value of stock awards granted prior to the adoption of ASU 2018-07 | ||||
| Risk-free interest rate | 2.02% | |||
| Expected volatility | 74.00% | |||
| Expected term (in years) | 6 years | |||
| Fair value of common stock | $ 0.19 | |||
| ASU 2018-07 | Maximum | ||||
| Fair value of stock awards granted prior to the adoption of ASU 2018-07 | ||||
| Risk-free interest rate | 2.31% | |||
| Expected volatility | 85.00% | |||
| Expected term (in years) | 10 years | |||
| Fair value of common stock | $ 6.28 | |||