Revenues - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales	$ 112,844	$ 99,705	$ 98,244	$ 92,834	$ 106,423	$ 90,250	$ 82,682	$ 81,562	$ 403,627	$ 360,917	$ 325,584
United States
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales									156,242	141,595	133,924
EMEA
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales									127,261	115,061	101,751
APAC
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales									105,038	90,730	78,094
Other Americas
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales									15,086	13,531	11,815
Service
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales									92,525	82,995	69,574
Service | Product or service transferred to customers at a point in time
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales									42,932	36,164	31,529
Service | Product or service transferred to customers over time
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales									49,593	46,831	38,045
Product
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales									311,102	277,922	256,010
Product | Product or service transferred to customers at a point in time
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales									311,102	277,922	256,010
Product | Product or service transferred to customers over time
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales									$ 0	$ 0	$ 0