FAIR VALUE - Financial Instruments Held by Consolidated Funds (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment, at fair value	$ 38,764,427	$ 38,372,626
Securities sold short – equities	(120,598)	(126,530)
Options written [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets, at fair value	287	5,520
Swaps (net)-corporate debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets, at fair value	83,432	39,166
Forward contracts (net) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities, at fair value	(132,386)	(93,863)
Futures [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets, at fair value	844	90
Corporate debt - bank debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment, at fair value	10,349,718	9,666,167
Corporate debt - all other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment, at fair value	7,814,118	9,822,570
Equities - common stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment, at fair value	11,842,043	12,519,258
Equities - preferred stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment, at fair value	871,896	654,749
Real estate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment, at fair value	5,890,050	3,946,142
Real estate loan portfolio [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment, at fair value	1,979,132	1,737,822
Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment, at fair value	17,470	25,918
Level I [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment, at fair value	4,694,907	3,367,195
Securities sold short – equities	(120,598)	(126,530)
Level I [Member] | Options written [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets, at fair value	0	0
Level I [Member] | Swaps (net)-corporate debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets, at fair value	0	0
Level I [Member] | Forward contracts (net) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities, at fair value	0	0
Level I [Member] | Futures [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets, at fair value	844	90
Level I [Member] | Corporate debt - bank debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment, at fair value	0	0
Level I [Member] | Corporate debt - all other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment, at fair value	0	0
Level I [Member] | Equities - common stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment, at fair value	4,689,131	3,362,742
Level I [Member] | Equities - preferred stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment, at fair value	3,888	2,520
Level I [Member] | Real estate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment, at fair value	0	0
Level I [Member] | Real estate loan portfolio [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment, at fair value	0	0
Level I [Member] | Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment, at fair value	1,888	1,933
Level II [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment, at fair value	13,938,266	15,142,246
Securities sold short – equities	0	0
Level II [Member] | Options written [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets, at fair value	287	5,520
Level II [Member] | Swaps (net)-corporate debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets, at fair value	8,635
Derivative liabilities, at fair value		(5,539)
Level II [Member] | Forward contracts (net) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities, at fair value	(132,386)	(93,863)
Level II [Member] | Futures [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets, at fair value	0	0
Level II [Member] | Corporate debt - bank debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment, at fair value	8,060,810	7,412,691
Level II [Member] | Corporate debt - all other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment, at fair value	5,152,485	6,663,519
Level II [Member] | Equities - common stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment, at fair value	683,956	1,055,465
Level II [Member] | Equities - preferred stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment, at fair value	5,208	2,133
Level II [Member] | Real estate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment, at fair value	34,340	0
Level II [Member] | Real estate loan portfolio [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment, at fair value	0	0
Level II [Member] | Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment, at fair value	1,467	8,438
Level III [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment, at fair value	20,131,254	19,863,185
Securities sold short – equities	0	0
Level III [Member] | Options written [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets, at fair value	0	0
Level III [Member] | Swaps (net)-corporate debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets, at fair value	74,797	44,705
Level III [Member] | Forward contracts (net) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities, at fair value	0	0
Level III [Member] | Futures [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets, at fair value	0	0
Level III [Member] | Corporate debt - bank debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment, at fair value	2,288,908	2,253,476
Level III [Member] | Corporate debt - all other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment, at fair value	2,661,633	3,159,051
Level III [Member] | Equities - common stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment, at fair value	6,468,956	8,101,051
Level III [Member] | Equities - preferred stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment, at fair value	862,800	650,096
Level III [Member] | Real estate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment, at fair value	5,855,710	3,946,142
Level III [Member] | Real estate loan portfolio [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment, at fair value	1,979,132	1,737,822
Level III [Member] | Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment, at fair value	$ 14,115	$ 15,547