Stock-Based Compensation - Employees, directors and non-employees (Details) - Market-Based Stock Options |
12 Months Ended |
|---|---|
Dec. 31, 2018 | |
| 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% |
| Derived service period (in years) | 2 years 3 months 18 days |