Revenues - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales	$ 93,491	$ 98,244	$ 187,108	$ 191,078
United States
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales	35,161	40,278	71,008	77,580
EMEA
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales	30,030	29,601	61,130	59,281
Other APAC
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales	15,387	15,799	30,429	31,900
China
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales	8,961	9,145	17,256	15,633
Other Americas
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales	3,952	3,421	7,285	6,684
Product sales
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales	67,992	75,720	136,792	146,301
Product sales | Product transferred to customers at a point in time
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales	67,992	75,720	136,792	146,301
Product sales | Product transferred to customers over time
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales	0	0	0	0
Service sales
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales	25,499	22,524	50,316	44,777
Service sales | Product transferred to customers at a point in time
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales	12,581	9,907	24,435	19,359
Service sales | Product transferred to customers over time
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales	$ 12,918	$ 12,617	$ 25,881	$ 25,418