Segment Information - Revenue Classified by Major Geographic Areas (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue	$ 242,556	$ 215,884	$ 477,086	$ 429,145
Americas [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue	234,471	204,052	460,083	407,715
Europe/Middle East
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue	7,222	10,904	14,745	19,364
Asia
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue	$ 863	$ 928	$ 2,258	$ 2,066