Revenue, deferred revenue, and deferred commissions - Consolidated Statement of Operations (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
Total revenue	$ 53,815			$ 50,781			$ 141,835	$ 130,849
Gross Profit	36,330			31,888			90,059	78,589
Operating expenses	32,314			30,289			96,970	91,990
Operating Income (Loss)	4,016			1,599			(6,911)	(13,401)
Net loss	4,161	$ (3,468)	$ (10,470)	298	$ (4,857)	$ (11,735)	(9,777)	(16,294)
Product
Revenue
Total revenue	28,510			28,511			70,311	65,646
Service
Revenue
Total revenue	$ 25,305			$ 22,270			$ 71,524	$ 65,203