INVESTMENTS - Fair Value, Additional Information (Details) - Consolidated Funds - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Schedule Of Investments In Marketable Securities [Line Items]
Securities sold short, proceeds	$ 78,187	$ 41,541
United States:
Schedule Of Investments In Marketable Securities [Line Items]
Total debt securities, cost	3,018,892	2,378,759
Total equity securities, cost	11,113	5,462
Europe:
Schedule Of Investments In Marketable Securities [Line Items]
Total debt securities, cost	1,386,171	1,214,068
Total equity securities, cost	1,872	1,494
Asia and other:
Schedule Of Investments In Marketable Securities [Line Items]
Total debt securities, cost	83,243	57,400
Total equity securities, cost	$ 206,335	$ 118,292