Income taxes - Schedule of Change in Valuation Allowance (Details) - Valuation Allowance of Deferred Tax Assets - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Increase (Decrease) in Valuation Allowance [Roll Forward]
Deferred tax asset valuation allowance, Balance at beginning of period	$ (79,788)	$ (94,575)	$ (98,755)
Additions	(45,833)	(7,008)	(23,789)
Deductions	1,654	21,795	27,969
Deferred tax asset valuation allowance, Balance at end of period	$ (123,967)	$ (79,788)	$ (94,575)