Stock-Based Compensation - Employees, directors and non-employees (Details) |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
|
| Fair value of stock-based awards granted to employees, directors, and, in 2018, non-employees, subsequent to the adoption of ASU 2018-07 | |||
| Expected volatility | 74.00% | 75.60% | 77.20% |
| Employees, directors and non-employees | |||
| Fair value of stock-based awards granted to employees, directors, and, in 2018, non-employees, subsequent to the adoption of ASU 2018-07 | |||
| Risk-free interest rate | 2.71% | 2.05% | 1.81% |
| Expected term (in years) | 6 years 2 months 16 days | 6 years 4 months 21 days | 6 years 3 months |
| Market-Based Stock Options | |||
| Fair value of stock-based awards granted to employees, directors, and, in 2018, non-employees, subsequent to the adoption of ASU 2018-07 | |||
| Risk-free interest rate | 3.15% | ||
| Expected volatility | 69.00% | ||
| Expected term (in years) | 2 years 3 months 18 days | ||