Stockholders' Equity - Stock-Based Compensation (Details) - USD ($) $ in Thousands |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2020 |
Sep. 30, 2019 |
Sep. 30, 2020 |
Sep. 30, 2019 |
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||||
| Total stock-based compensation expense | $ 725 | $ 833 | $ 2,095 | $ 2,444 |
| Research and development [Member] | ||||
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||||
| Total stock-based compensation expense | 157 | 179 | 462 | 559 |
| General and administrative [Member] | ||||
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||||
| Total stock-based compensation expense | $ 568 | $ 654 | $ 1,633 | $ 1,885 |