INVESTMENTS - Fair Value (Details) - Consolidated Funds - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 4,945,969	$ 3,672,118
Equity securities	$ 249,556	$ 136,116
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	95.20%	96.40%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	4.80%	3.60%
Investments, at fair value	$ 5,195,525	$ 3,808,234
Investments, at fair value, Fair Value as a Percentage of Investments of Consolidated Funds	100.00%	100.00%
Total securities sold short, at fair value	$ (74,228)	$ (41,016)
Equity securities
Schedule Of Investments In Marketable Securities [Line Items]
Total securities sold short, at fair value	(74,228)	(41,016)
United States
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	3,215,465	2,392,717
Equity securities	$ 12,941	$ 7,725
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	62.00%	62.90%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.20%	0.20%
United States | Consumer discretionary
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 742,463	$ 628,621
Equity securities	$ 2,032	$ 711
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	14.30%	16.50%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.00%	0.00%
United States | Consumer staples
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 125,829	$ 123,395
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	2.40%	3.20%
United States | Energy
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 97,887	$ 55,655
Equity securities	$ 1,865	$ 2,002
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	1.90%	1.50%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.00%	0.10%
United States | Financials
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 292,701	$ 182,685
Equity securities	$ 7,912	$ 3,977
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	5.60%	4.80%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.20%	0.10%
United States | Government
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 1,516	$ 5,234
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.00%	0.10%
United States | Health care
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 445,347	$ 337,138
Equity securities	$ 320	$ 343
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	8.60%	8.90%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.00%	0.00%
United States | Industrials
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 439,609	$ 379,122
Equity securities	$ 406	$ 1
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	8.50%	10.00%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.00%	0.00%
United States | Information technology
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 445,148	$ 272,637
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	8.60%	7.20%
United States | Materials
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 358,342	$ 237,417
Equity securities	$ 138	$ 691
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	6.90%	6.20%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.00%	0.00%
United States | Telecommunication services
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 154,516	$ 93,893
Equity securities	$ 268	$ 0
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	3.00%	2.50%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.00%	0.00%
United States | Utilities
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 112,107	$ 76,920
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	2.20%	2.00%
Europe
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 1,672,884	$ 1,226,100
Equity securities	$ 11,815	$ 1,605
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	32.10%	32.10%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.30%	0.00%
Europe | Consumer discretionary
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 494,501	$ 374,627
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	9.50%	9.80%
Europe | Consumer staples
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 102,862	$ 92,750
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	2.00%	2.40%
Europe | Energy
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 6,314	$ 13,274
Equity securities	$ 3,032	$ 0
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.10%	0.30%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.10%	0.00%
Europe | Financials
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 28,858	$ 13,822
Equity securities	$ 4,081	$ 1,605
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.60%	0.40%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.10%	0.00%
Europe | Government
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 0	$ 1,996
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.00%	0.10%
Europe | Health care
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 319,397	$ 210,078
Equity securities	$ 635	$ 0
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	6.10%	5.50%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.00%	0.00%
Europe | Industrials
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 145,796	$ 54,578
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	2.80%	1.40%
Europe | Information technology
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 57,092	$ 23,832
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	1.10%	0.60%
Europe | Materials
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 282,079	$ 226,961
Equity securities	$ 4,067	$ 0
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	5.40%	6.00%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.10%	0.00%
Europe | Telecommunication services
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 234,445	$ 214,182
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	4.50%	5.60%
Europe | Utilities
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 1,540	$ 0
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.00%	0.00%
Asia and other
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 57,620	$ 53,301
Equity securities	$ 224,800	$ 126,786
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	1.10%	1.40%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	4.30%	3.40%
Asia and other | Consumer discretionary
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 2,720	$ 3,145
Equity securities	$ 17,337	$ 7,639
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.10%	0.10%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.30%	0.20%
Asia and other | Consumer staples
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 2,238	$ 5,994
Equity securities	$ 6,837	$ 3,786
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.00%	0.20%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.10%	0.10%
Asia and other | Energy
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 5,022	$ 9,570
Equity securities	$ 5,731	$ 6,978
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.10%	0.30%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.10%	0.20%
Asia and other | Financials
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 4,305	$ 0
Equity securities	$ 104,569	$ 44,328
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.10%	0.00%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	2.00%	1.20%
Asia and other | Government
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 0	$ 1,506
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.00%	0.00%
Asia and other | Health care
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 1,185	$ 1,245
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.00%	0.00%
Asia and other | Industrials
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 18,119	$ 15,450
Equity securities	$ 45,173	$ 21,564
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.30%	0.40%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.90%	0.60%
Asia and other | Information technology
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 447	$ 409
Equity securities	$ 20,948	$ 16,642
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.00%	0.00%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.40%	0.40%
Asia and other | Materials
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 8,013	$ 10,245
Equity securities	$ 17,744	$ 19,697
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.20%	0.30%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.30%	0.50%
Asia and other | Telecommunication services
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 15,571	$ 4,809
Equity securities	$ 3,316	$ 4,296
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.30%	0.10%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.10%	0.10%
Asia and other | Utilities
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 0	$ 928
Equity securities	$ 3,145	$ 1,856
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.00%	0.00%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.10%	0.10%