Revenue, deferred revenue, and deferred commissions - Significant Changes in Deferred Revenue (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2020	Jun. 30, 2019
Revenue from Contract with Customer [Abstract]
Revenue recognized pertaining to amounts deferred as of Beginning of Period		$ 34,200
Revenue recognized pertaining to amounts deferred as of End of Period	$ 17,000		$ 29,400
Change in Contract with Customer, Liability [Roll Forward]
Beginning balance	56,676	61,475
Additions	17,385	32,330
Revenue Recognized	(20,047)	(39,791)
Ending balance	$ 54,014	$ 54,014