Accrued expenses and other current liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Accrued expenses and other current liabilities
Accrued clinical and development expenditure	$ 9,491	$ 8,782
Accrued employee expenses	3,814	6,863
Other accrued expenditure	2,562	2,662
Accrued purchase commitments	2,500	5,000
Other	135	56
Total	$ 18,502	$ 23,363