Segment Information - Revenue Classified by Major Geographic Areas (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue	$ 251,770	$ 234,530
Americas [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue	243,399	225,612
Europe/Middle East
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue	7,669	7,523
Asia
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue	$ 702	$ 1,395