Accrued expenses and other payables - Warranty (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Accrued expenses and other payables
Balance at beginning of the period	$ 34,031	$ 30,936	$ 32,907	$ 31,085
Additions during the period	3,947	4,563	12,303	12,064
Settlement within the period	(4,480)	(4,338)	(11,218)	(11,921)
Foreign currency translation loss/(gain)	1,339	(874)	845	(941)
Balance at end of the period	$ 34,837	$ 30,287	$ 34,837	$ 30,287