Segment Operating Results - Revenues Derived from Clients by Geographical Areas (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting Information [Line Items]
Net Revenues	$ 397,953	$ 375,404	$ 1,326,606	$ 1,286,093
United States [Member]
Segment Reporting Information [Line Items]
Net Revenues	317,203	290,944	977,870	1,023,686
Europe and Other [Member]
Segment Reporting Information [Line Items]
Net Revenues	77,779	82,063	337,207	239,226
Latin America [Member]
Segment Reporting Information [Line Items]
Net Revenues	$ 2,971	$ 2,397	$ 11,529	$ 23,181