Segment Information - Revenue Classified by Major Geographic Areas (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	$ 226,220	$ 211,804	$ 655,365	$ 638,834
Americas [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	217,900	199,878	625,615	606,168
Europe / Middle East [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	7,655	11,118	27,019	30,150
Asia [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	$ 665	$ 808	$ 2,731	$ 2,516