Stock-Based Compensation - Compensation expense (Details) - USD ($) $ in Thousands |
3 Months Ended | 9 Months Ended | |||
|---|---|---|---|---|---|
Sep. 30, 2019 |
Sep. 30, 2019 |
Sep. 30, 2018 |
Sep. 30, 2019 |
Sep. 30, 2018 |
|
| Stock-based compensation expense | |||||
| Stock-based compensation expense | $ 10,358 | $ 9,887 | $ 30,440 | $ 18,402 | |
| Unrecognized compensation cost | $ 76,900 | 76,900 | 76,900 | ||
| Unrecognized compensation cost expected to be recognized over a weighted average period | 2 years 3 months 18 days | ||||
| Research and development expenses | |||||
| Stock-based compensation expense | |||||
| Stock-based compensation expense | 2,195 | 1,347 | 6,798 | 2,331 | |
| General and administrative expenses | |||||
| Stock-based compensation expense | |||||
| Stock-based compensation expense | $ 8,163 | $ 8,540 | $ 23,642 | $ 16,071 | |