Prepaid expenses and other current assets (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Prepaid expenses and other current assets
Prepaid clinical	$ 3,719	$ 728
Prepaid insurance	994	673
Prepaid Manufacturing Cost	558
Other prepaid expenses and current assets	366	383
Total prepaid expenses and other current assets	$ 5,637	$ 1,784