Segment and Geographical Information - Geographical Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information
Total revenues	$ 787,309	$ 712,714	$ 695,908
Total property and equipment, net	51,500	42,595	42,011
United States
Segment Reporting Information
Total revenues	685,881	613,817	594,851
Total property and equipment, net	44,684	34,899	36,497
Non-US
Segment Reporting Information
Total revenues	101,428	98,897	101,057
Total property and equipment, net	$ 6,816	$ 7,696	$ 5,514