Segment Information - Revenue Classified by Major Geographic Areas (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue	$ 234,530	$ 213,261
Americas [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue	225,612	203,663
Europe/Middle East
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue	7,523	8,460
Asia
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue	$ 1,395	$ 1,138