Income taxes - Provision for Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Current:
Federal	$ 0	$ 0	$ 0
State	183	63	83
Foreign	1,149	2,937	1,292
Total current income tax expense	1,332	3,000	1,375
Deferred:
Federal	0	0	0
State	0	0	0
Foreign	(149)	149	0
Total deferred income tax expense	(149)	149	0
Total provision for income taxes	$ 1,183	$ 3,149	$ 1,375