Revenue, deferred revenue, and deferred commissions - Consolidated Statement of Operations (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue
Total revenue	$ 49,652	$ 50,781	$ 44,759	$ 35,309	$ 48,880	$ 47,822	$ 42,686	$ 40,242	$ 180,501	$ 179,630	$ 165,989
Gross Profit	30,510	31,888	27,016	19,685	31,197	31,138	25,651	23,901	109,099	111,887	101,062
Operating expenses									123,222	118,192	111,762
Loss from Operations									(14,123)	(6,305)	(10,700)
Net loss	$ (1,686)	$ 298	$ (4,857)	$ (11,735)	$ (1,101)	$ (249)	$ (3,554)	$ (4,770)	(17,980)	(9,674)	(10,897)
Earnings Per Share, Basic and Diluted	$ (0.05)	$ 0.01	$ (0.16)	$ (0.38)
Earnings Per Share, Diluted	$ (0.05)	$ 0.01	$ (0.16)	$ (0.38)
Product
Revenue
Total revenue									92,561	97,447	91,585
Service
Revenue
Total revenue									87,940	82,183	74,404
Product Segment | Software [Member]
Revenue
Total revenue									31,337	37,317	29,839
Product Segment | Device [Member]
Revenue
Total revenue									61,224	60,130	61,746
Service Segment
Revenue
Total revenue									87,940	82,183	74,404
Service Segment | Professional Services and Training [Member]
Revenue
Total revenue									19,094	19,916	22,062
Service Segment | Maintenance and Support [Member]
Revenue
Total revenue									$ 68,846	$ 62,267	$ 52,342