Share-based compensation - Share-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Total share-based compensation expense included in the consolidated statements of operations
Total share-based compensation expense	$ 1,448	$ 3,479
Research and development
Total share-based compensation expense included in the consolidated statements of operations
Total share-based compensation expense	978	2,021
General and administrative
Total share-based compensation expense included in the consolidated statements of operations
Total share-based compensation expense	$ 470	$ 1,458