Segment Operating Results - Revenues Derived from Clients by Geographical Areas (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Net Revenues	$ 2,291,628	$ 1,983,383	$ 2,063,425
United States [Member]
Segment Reporting Information [Line Items]
Net Revenues	1,767,976	1,464,551	1,591,883
Europe And Other [Member]
Segment Reporting Information [Line Items]
Net Revenues	497,102	501,425	438,602
Latin America [Member]
Segment Reporting Information [Line Items]
Net Revenues	$ 26,550	$ 17,407	$ 32,940