Revenue, deferred revenue, and deferred commissions - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenue	$ 53,815	$ 50,781	$ 141,835	$ 130,849
Product Segment [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenue	28,510	28,511	70,311	65,646
Product Segment [Member] | Software [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenue	11,483	9,509	22,281	22,080
Product Segment [Member] | Device [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenue	17,027	19,002	48,030	43,566
Service Segment [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenue	25,305	22,270	71,524	65,203
Service Segment [Member] | Maintenance and Support [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenue	20,387	17,538	57,450	50,859
Service Segment [Member] | Professional Services and Training [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenue	$ 4,918	$ 4,732	$ 14,074	$ 14,344