Revenue, deferred revenue, and deferred commissions - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Jun. 30, 2020	Dec. 31, 2019
Revenue from Contract with Customer [Abstract]
Payment terms on invoiced amounts			30 days
Deferred commissions	$ 11,325		$ 11,325		$ 11,118	$ 10,477
Percentage of deferred commissions to be recognized as commission expense in the next 12 months	49.00%		49.00%
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
Deferred revenue and backlog	$ 139,400		$ 139,400
Percentage of deferred revenue to be recognized over the next 12 months	70.00%		70.00%
Contract with Customer, Asset, before Allowance for Credit Loss	$ 4,500		$ 4,500			$ 4,300