Accrued expenses and other current liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
Accrued expenses and other current liabilities
Accrued employee compensation and benefits	$ 740		$ 1,606
Accrued external research and development expenses	4,998		6,361
Accrued legal and professional fees	657		370
Operating lease liability	230	$ 224
Other	126		85
Total accrued expenses and other current liabilities	$ 6,751		$ 8,422