Revenue, deferred revenue, and deferred commissions - Significant Changes in Deferred Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenue from Contract with Customer [Abstract]
Revenue recognized pertaining to amounts deferred as of Beginning of Period	$ 18,500		$ 46,000
Revenue recognized pertaining to amounts deferred as of End of Period		$ 17,200		$ 40,000
Change in Contract with Customer, Liability [Roll Forward]
Beginning balance	54,014		61,475
Additions	25,866		58,197
Revenue Recognized	(22,472)		(62,264)
Ending balance	$ 57,408		$ 57,408