INVESTMENTS - Fair Value (Details) - Consolidated Funds - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 6,116,657	$ 6,995,677
Equity securities	$ 365,037	$ 131,991
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	90.60%	95.10%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	5.40%	1.80%
Real estate securities	$ 272,452	$ 230,741
Real estate securities, Fair Value as a Percentage of Investments of Consolidated Funds	4.00%	3.10%
Total Level III investments	$ 6,754,146	$ 7,358,409
Total investments, at fair value, percentage	100.00%	100.00%
United states
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 3,343,555	$ 3,960,403
Total debt securities, cost	3,898,370	3,981,956
Equity securities	100,524	131,897
Total equity securities, cost	$ 138,387	$ 137,149
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	49.40%	53.90%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	1.50%	1.80%
Real estate securities	$ 272,452	$ 230,741
Real estate securities, cost	$ 272,433	$ 230,741
Real estate securities, Fair Value as a Percentage of Investments of Consolidated Funds	4.00%	3.10%
United states | Communication services
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 414,411	$ 464,356
Equity securities	$ 96	$ 312
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	6.10%	6.40%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.00%	0.00%
United states | Consumer discretionary
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 395,933	$ 508,701
Equity securities	$ 399	$ 658
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	5.90%	6.90%
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	$ 83,805	$ 92,102
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	1.20%	1.30%
United states | Energy
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 139,358	$ 223,671
Equity securities	$ 164	$ 256
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	2.10%	3.00%
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	$ 322,200	$ 355,113
Equity securities	$ 9	$ 0
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	4.80%	4.80%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.00%	0.00%
Real estate securities	$ 3,048	$ 0
Real estate 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	$ 408,204	$ 512,864
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	6.00%	7.00%
United states | Industrials
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 515,056	$ 563,920
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	7.60%	7.70%
United states | Information technology
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 435,559	$ 524,390
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	6.40%	7.10%
United states | Materials
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 245,224	$ 294,300
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	3.60%	4.00%
United states | Real estate
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 188,440	$ 204,933
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	2.80%	2.80%
Real estate securities	$ 269,404	$ 230,741
Real estate securities, Fair Value as a Percentage of Investments of Consolidated Funds	4.00%	3.10%
United states | Utilities
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 195,365	$ 216,053
Equity securities	$ 99,856	$ 130,671
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	2.90%	2.90%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	1.50%	1.80%
Europe
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 2,617,924	$ 2,870,174
Total debt securities, cost	3,051,994	2,876,531
Equity securities	264,513	94
Total equity securities, cost	$ 264,908	$ 1,227
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	38.60%	39.00%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	3.90%	0.00%
Europe | Communication services
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 438,481	$ 469,822
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	6.50%	6.40%
Europe | Consumer discretionary
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 541,908	$ 659,001
Equity securities	$ 46,181	$ 94
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	8.00%	9.00%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.70%	0.00%
Europe | Consumer staples
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 175,128	$ 178,609
Equity securities	$ 337	$ 0
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	2.60%	2.40%
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	$ 5,764	$ 11,316
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.10%	0.20%
Europe | Financials
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 95,392	$ 101,933
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	1.40%	1.40%
Europe | Health care
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 522,664	$ 579,765
Equity securities	$ 1,676	$ 0
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	7.70%	7.90%
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	$ 313,784	$ 362,120
Equity securities	$ 189,717	$ 0
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	4.60%	4.90%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	2.80%	0.00%
Europe | Information technology
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 212,444	$ 177,152
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	3.10%	2.40%
Europe | Materials
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 210,159	$ 230,289
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	3.10%	3.10%
Europe | Real estate
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 97,655	$ 96,315
Equity securities	$ 26,602	$ 0
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	1.40%	1.30%
Equity securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.40%	0.00%
Europe | Utilities
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 4,545	$ 3,852
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.10%	0.10%
Asia and other
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 155,178	$ 165,100
Total debt securities, cost	$ 186,212	$ 164,650
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	2.30%	2.20%
Asia and other | Communication services
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 17,061	$ 15,750
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	$ 31,759	$ 40,073
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.50%	0.50%
Asia and other | Consumer staples
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 12,859	$ 11,545
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.20%	0.20%
Asia and other | Energy
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 16,802	$ 13,471
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.20%	0.10%
Asia and other | Financials
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 8,423	$ 10,313
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.10%	0.10%
Asia and other | Government
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 0	$ 917
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	$ 6,342	$ 8,923
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	$ 41,045	$ 31,814
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.60%	0.40%
Asia and other | Information technology
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 2,532	$ 5,639
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.00%	0.10%
Asia and other | Materials
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 5,219	$ 5,604
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.10%	0.10%
Asia and other | Real estate
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 738	$ 751
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.00%	0.00%
Asia and other | Utilities
Schedule Of Investments In Marketable Securities [Line Items]
Debt securities	$ 12,398	$ 20,300
Debt securities, Fair Value as a Percentage of Investments of Consolidated Funds	0.20%	0.30%