Segment Operating Results - Revenues Derived from Clients and Private Equity Funds by Geographical Areas (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Net Revenues	$ 1,636,853	$ 1,439,905	$ 1,228,989
United States [Member]
Segment Reporting Information [Line Items]
Net Revenues	1,199,236	1,056,796	900,672
Europe and Other [Member]
Segment Reporting Information [Line Items]
Net Revenues	422,322	338,285	287,884
Latin America [Member]
Segment Reporting Information [Line Items]
Net Revenues	$ 15,295	$ 44,824	$ 40,433