Segment Information - Revenue Classified by Major Geographic Areas (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue	$ 234,793	$ 237,814	$ 737,498	$ 714,900
Americas [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue	227,001	230,486	712,864	690,569
Europe/Middle East
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue	7,257	6,500	22,592	21,245
Asia
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue	$ 535	$ 828	$ 2,042	$ 3,086