Revenue, deferred revenue, and deferred commissions - Cash Flows From Operating Activities (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net loss	$ (3,468)	$ (10,470)	$ (4,857)	$ (11,735)	$ (13,938)	$ (16,592)
Adjustments to reconcile net loss to net cash used in operating activities:
Deferred commissions					(640)	385
Deferred revenue					$ (7,461)	$ (6,027)