Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands |
Dec. 31, 2020 |
Dec. 31, 2019 |
|---|---|---|
| Accrued Expenses and Other Current Liabilities | ||
| Accrued employee compensation and benefits | $ 8,124 | $ 5,045 |
| Accrued external research and development expenses | 3,156 | 6,715 |
| Accrued manufacturing facility expenses | 339 | 2,824 |
| Accrued general and administrative expenses | 1,244 | 1,136 |
| Other | 554 | 322 |
| Accrued expenses and other current liabilities | $ 13,417 | $ 16,042 |