Income taxes - Valuation Allowances (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Deferred Tax Assets, Valuation Allowance [Roll Forward]
Beginning at beginning of period	$ 43,467	$ 45,661	$ 125,894
Additions to valuation allowance	6,108	3,719	9,545
Reductions to valuation allowance	(7,646)	(5,913)	(89,778)
Balance at the end of the period	$ 41,929	$ 43,467	$ 45,661