Revenue, deferred revenue, and deferred commissions - Cash Flows From Operating Activities (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net loss	$ 4,161	$ (3,468)	$ (10,470)	$ 298	$ (4,857)	$ (11,735)	$ (9,777)	$ (16,294)
Adjustments to reconcile net loss to net cash used in operating activities:
Deferred commissions							(847)	336
Deferred revenue							$ (5,227)	$ (2,453)