INVESTMENTS - Fair Value (Details) - Consolidated Funds - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 6,834,078	$ 6,502,413
Equity securities	$ 48,346	$ 28,972
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	98.50%	99.50%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.70%	0.50%
Real estate securities	$ 57,080	$ 0
Real estate securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.80%	0.00%
Total Level III investments	$ 6,939,504	$ 6,531,385
Total investments, at fair value, percentage	100.00%	100.00%
Equity securities sold short	$ 0	$ (2,609)
United States
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	4,014,772	3,860,665
Equity securities	$ 5,406	$ 5,426
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	57.90%	59.10%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.10%	0.10%
Real estate securities	$ 57,080	$ 0
Real estate securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.80%	0.00%
United States | Communication services
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 562,588	$ 543,948
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	8.10%	8.40%
United States | Consumer discretionary
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 463,591	$ 506,551
Equity securities	$ 2,314	$ 1,915
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	6.70%	7.80%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.10%	0.10%
United States | Consumer staples
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 73,446	$ 112,197
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	1.10%	1.70%
United States | Energy
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 294,600	$ 204,568
Equity securities	$ 122	$ 131
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	4.20%	3.10%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.00%	0.00%
United States | Financials
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 347,654	$ 332,240
Equity securities	$ 415	$ 837
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	5.00%	5.10%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.00%	0.00%
United States | Health care
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 497,827	$ 537,592
Equity securities	$ 1,383	$ 1,348
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	7.20%	8.20%
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	$ 506,454	$ 443,406
Equity securities	$ 100	$ 88
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	7.30%	6.80%
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	$ 517,714	$ 536,000
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	7.50%	8.20%
United States | Materials
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 299,226	$ 289,499
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	4.30%	4.40%
United States | Real estate
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 261,778	$ 217,633
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	3.80%	3.30%
United States | Utilities
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 189,894	$ 137,031
Equity securities	$ 1,072	$ 1,107
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	2.70%	2.10%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.00%	0.00%
Europe
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 2,631,955	$ 2,413,280
Equity securities	$ 40,783	$ 986
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	37.90%	36.90%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.60%	0.10%
Europe | Communication services
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 562,857	$ 530,337
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	8.20%	8.10%
Europe | Consumer discretionary
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 570,296	$ 545,324
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	8.20%	8.30%
Europe | Consumer staples
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 155,299	$ 160,406
Equity securities	$ 0	$ 38
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	2.20%	2.50%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.00%	0.00%
Europe | Energy
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 11,124	$ 15,260
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.20%	0.20%
Europe | Financials
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 69,965	$ 48,545
Equity securities	$ 39,860	$ 0
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	1.00%	0.70%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.60%	0.00%
Europe | Health care
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 506,629	$ 418,516
Equity securities	$ 923	$ 948
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	7.30%	6.40%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.00%	0.10%
Europe | Industrials
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 280,831	$ 246,640
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	4.00%	3.80%
Europe | Information technology
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 175,777	$ 194,988
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	2.50%	3.00%
Europe | Materials
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 268,538	$ 221,660
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	3.90%	3.40%
Europe | Real estate
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 27,598	$ 30,045
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.40%	0.50%
Europe | Utilities
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 3,041	$ 1,559
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	$ 187,351	$ 228,468
Equity securities	$ 2,157	$ 22,560
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	2.70%	3.50%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.00%	0.30%
Asia and other | Communication services
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 18,528	$ 12,069
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.30%	0.20%
Asia and other | Consumer discretionary
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 45,019	$ 36,822
Equity securities	$ 0	$ 874
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.60%	0.60%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.00%
Asia and other | Consumer staples
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 3,765	$ 11,867
Equity securities	$ 15	$ 997
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.10%	0.20%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.00%	0.00%
Asia and other | Energy
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 18,786	$ 20,594
Equity securities	$ 355	$ 382
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.30%	0.30%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.00%	0.00%
Asia and other | Financials
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 5,464	$ 13,995
Equity securities	$ 0	$ 2,935
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.10%	0.20%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.00%	0.00%
Asia and other | Government
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 5,708	$ 12,155
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.10%	0.20%
Asia and other | Health care
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 6,952	$ 9,633
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.10%	0.10%
Asia and other | Industrials
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 45,829	$ 40,468
Equity securities	$ 0	$ 11,265
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.50%	0.70%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.00%	0.20%
Asia and other | Information technology
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 3,519	$ 1,887
Equity securities	$ 0	$ 1,725
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	0.00%	0.00%
Asia and other | Materials
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 14,410	$ 15,516
Equity securities	$ 1,787	$ 4,382
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.20%	0.20%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.00%	0.10%
Asia and other | Real estate
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 721	$ 38,592
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.00%	0.60%
Asia and other | Utilities
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 18,650	$ 14,870
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.30%	0.20%