Share-based compensation - Allocation of Compensation Expense Related to Restricted Shares (Details) - Non-Vested Restricted Shares - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Compensation expense	$ 3,381	$ 1,615	$ 8,155	$ 4,687
Selling, General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Compensation expense	2,028	1,065	5,078	3,179
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Compensation expense	$ 1,353	$ 550	$ 3,077	$ 1,508