Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands |
Dec. 31, 2019 |
Dec. 31, 2018 |
|---|---|---|
| Accrued Expenses and Other Current Liabilities | ||
| Accrued employee compensation and benefits | $ 5,045 | $ 3,377 |
| Accrued external research and development expenses | 6,715 | 2,252 |
| Accrued manufacturing facility expenses | 2,824 | |
| Accrued general and administrative expenses | 1,136 | 1,676 |
| Accrued lease liability, current portion | 4,502 | |
| Other | 322 | 311 |
| Accrued expenses and other current liabilities | $ 16,042 | $ 12,118 |