Stock-Based Compensation - Compensation expense (Details) - USD ($) $ in Thousands |
3 Months Ended | |
|---|---|---|
Mar. 31, 2020 |
Mar. 31, 2019 |
|
| Stock-based compensation expense | ||
| Stock-based compensation expense | $ 8,488 | $ 9,478 |
| Unrecognized compensation cost | $ 68,400 | |
| 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 | $ 2,111 | 1,991 |
| General and administrative expenses | ||
| Stock-based compensation expense | ||
| Stock-based compensation expense | $ 6,377 | $ 7,487 |