Summary of significant accounting policies - Contract Balances (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Accounting Policies [Abstract]
Contract with customer, asset	$ 1,700		$ 1,700		$ 900
Contract With Customer, Liability [Roll Forward]
Balance, beginning of the period	238,457	$ 157,282	205,509	$ 140,449
Acquisitions	5,200	0	5,200	0
Revenue earned	(71,574)	(49,823)	(144,038)	(115,784)
Deferral of revenue	98,284	80,179	203,696	162,973
Balance, end of the period	$ 270,367	$ 187,638	$ 270,367	$ 187,638