Revenues - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales	$ 93,617	$ 92,834
United States
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales	35,848	37,302
EMEA
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales	31,100	29,680
APAC
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales	23,337	22,589
Other Americas
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales	3,332	3,263
Product sales
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales	68,800	70,581
Product sales | Product transferred to customers at a point in time
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales	68,800	70,581
Product sales | Product transferred to customers over time
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales	0	0
Service sales
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales	24,817	22,253
Service sales | Product transferred to customers at a point in time
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales	11,854	9,452
Service sales | Product transferred to customers over time
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales	$ 12,963	$ 12,801