Segment Information - Revenue Classified by Major Geographic Areas (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue	$ 250,935	$ 242,556	$ 502,705	$ 477,086
Americas [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue	242,464	234,471	485,863	460,083
Europe/Middle East
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue	7,666	7,222	15,335	14,745
Asia
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue	$ 805	$ 863	$ 1,507	$ 2,258