Share-based compensation - Schedule of share-based comp expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share compensation expenses	$ 1,587	$ 3,954	$ 3,153	$ 5,412
Restricted shares with service condition
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share compensation expenses	667	940	1,174	1,134
Restricted shares with service and performance condition
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share compensation expenses	$ 920	$ 3,014	$ 1,979	$ 4,278