Stockholders' Equity - Share-Based Compensation (Details) - USD ($) $ in Thousands |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2019 |
Dec. 31, 2018 |
Dec. 31, 2017 |
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
| Share-based compensation expense | $ 24,515 | $ 20,846 | $ 24,915 |
| Research and development expenses | |||
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
| Share-based compensation expense | 9,641 | 8,352 | 14,235 |
| General and administrative expenses | |||
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
| Share-based compensation expense | $ 14,874 | $ 12,494 | $ 10,680 |