Stockholders' Equity - Stock-Based Compensation (Details) - USD ($) $ in Thousands |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2020 |
Jun. 30, 2019 |
Jun. 30, 2020 |
Jun. 30, 2019 |
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||||
| Total stock-based compensation expense | $ 731 | $ 813 | $ 1,370 | $ 1,611 |
| Research and development [Member] | ||||
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||||
| Total stock-based compensation expense | 161 | 184 | 305 | 380 |
| General and administrative [Member] | ||||
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||||
| Total stock-based compensation expense | $ 570 | $ 629 | $ 1,065 | $ 1,231 |