Income taxes - Schedule of Valuation Allowances (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Deferred Tax Assets, Valuation Allowance [Roll Forward]
Beginning at beginning of period	$ 45,661	$ 125,894	$ 136,418
Additions to valuation allowance	3,719	9,545	3,908
Reductions to valuation allowance	(5,913)	(89,778)	(14,432)
Balance at the end of the period	$ 43,467	$ 45,661	$ 125,894