Accrued Expenses - Summary (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Accrued expenses
Accrued accounts payable	$ 1,275	$ 4,251
Compensation expense	2,656	2,870
Research and development fees	1,833	1,048
Lease liabilities	934	733
Audit and tax fees	126	522
Other current liabilities	664	520
Total	$ 7,488	$ 9,944