Accrued Expenses (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Accrued Expenses
Payroll and related costs	$ 2,533	$ 4,097
Clinical trials and drug development	6,645	2,452
Professional fees	1,158	927
Short-term lease liabilities	519	510
Other	99	532
Total accrued expenses	$ 10,954	$ 8,518