Revenue, deferred revenue, and deferred commissions - Consolidated Statement of Operations (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
Total revenue	$ 47,347		$ 44,759		$ 88,020	$ 80,068
Gross Profit	29,943		27,016		53,729	46,701
Operating expenses	32,270		30,956		64,656	61,701
Operating Income (Loss)	(2,327)		(3,940)		(10,927)	(15,000)
Net loss	(3,468)	$ (10,470)	(4,857)	$ (11,735)	(13,938)	(16,592)
Product
Revenue
Total revenue	23,951		23,132		41,801	37,135
Service
Revenue
Total revenue	$ 23,396		$ 21,627		$ 46,219	$ 42,933