Revenue - Disaggregation of revenue (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenue
Revenue	$ 52,928	$ 51,439	$ 54,954	$ 56,370	$ 70,531	$ 79,691	$ 56,167	$ 47,095	$ 215,691	$ 253,484	$ 211,336
Percent of Total									100.00%	100.00%	100.00%
Products and Licenses transferred at a point in time
Revenue
Revenue									$ 132,986	$ 183,313	$ 152,054
Services transferred over time
Revenue
Revenue									82,705	70,171	59,282
EMEA
Revenue
Revenue									$ 117,086	$ 145,942	$ 102,349
Percent of Total									54.00%	58.00%	48.00%
Americas
Revenue
Revenue									$ 53,171	$ 61,577	$ 54,979
Percent of Total									25.00%	24.00%	26.00%
APAC
Revenue
Revenue									$ 45,434	$ 45,965	$ 54,008
Percent of Total									21.00%	18.00%	26.00%
Hardware products
Revenue
Revenue									$ 81,849	$ 127,005	$ 105,560
Software licenses
Revenue
Revenue									51,137	56,308	46,494
Subscription
Revenue
Revenue									27,788	22,280	15,432
Professional services
Revenue
Revenue									5,689	5,759	5,743
Maintenance, support and other
Revenue
Revenue									$ 49,228	$ 42,132	$ 38,107