FAIR VALUE - Valuation of Investments and Other Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Total investments	$ 39,911,888	$ 38,372,626
Securities sold short – equities	(140,251)	(126,530)
Options written (net)
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative assets, at fair value	14,991	5,520
Swaps (net)
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative assets, at fair value	11,222	39,166
Swaptions (net)
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative assets, at fair value	5,392
Forward contracts (net)
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative liabilities, at fair value	(83,481)	(93,863)
Futures (net)
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative assets, at fair value		90
Derivative liabilities, at fair value	(3,067)
Corporate debt – bank debt
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Total investments	10,161,566	9,666,167
Corporate debt – all other
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Total investments	7,558,623	9,822,570
Equities – common stock
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Total investments	12,613,353	12,519,258
Equities – Preferred Stock
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Total investments	932,355	654,749
Equities – preferred stock
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Total investments	6,258,478	3,946,142
Real estate loan portfolio
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Total investments	2,369,441	1,737,822
Other
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Total investments	18,072	25,918
Level I
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Total investments	4,811,623	3,367,195
Securities sold short – equities	(140,251)	(126,530)
Level I | Options written (net)
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative liabilities, at fair value	(1,862)	0
Level I | Swaps (net)
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative assets, at fair value	0
Derivative liabilities, at fair value		0
Level I | Swaptions (net)
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative assets, at fair value	0
Level I | Forward contracts (net)
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative assets, at fair value		0
Derivative liabilities, at fair value	0
Level I | Futures (net)
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative assets, at fair value		90
Derivative liabilities, at fair value	(3,067)
Level I | Corporate debt – bank debt
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Total investments	0	0
Level I | Corporate debt – all other
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Total investments	798	0
Level I | Equities – common stock
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Total investments	4,804,068	3,362,742
Level I | Equities – Preferred Stock
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Total investments	4,101	2,520
Level I | Equities – preferred stock
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Total investments	0	0
Level I | Real estate loan portfolio
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Total investments	0	0
Level I | Other
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Total investments	2,656	1,933
Level II
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Total investments	13,634,420	15,142,246
Securities sold short – equities	0	0
Level II | Options written (net)
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative assets, at fair value	16,853	5,520
Level II | Swaps (net)
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative assets, at fair value	11,222
Derivative liabilities, at fair value		(5,539)
Level II | Swaptions (net)
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative assets, at fair value	5,392
Level II | Forward contracts (net)
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative liabilities, at fair value	(83,481)	(93,863)
Level II | Futures (net)
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative assets, at fair value	0
Derivative liabilities, at fair value		0
Level II | Corporate debt – bank debt
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Total investments	7,352,129	7,412,691
Level II | Corporate debt – all other
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Total investments	5,125,646	6,663,519
Level II | Equities – common stock
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Total investments	1,109,270	1,055,465
Level II | Equities – Preferred Stock
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Total investments	8,483	2,133
Level II | Equities – preferred stock
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Total investments	37,184	0
Level II | Real estate loan portfolio
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Total investments	0	0
Level II | Other
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Total investments	1,708	8,438
Level III
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Total investments	21,465,845	19,863,185
Securities sold short – equities	0	0
Level III | Options written (net)
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative assets, at fair value	0
Derivative liabilities, at fair value		0
Level III | Swaps (net)
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative assets, at fair value	0	44,705
Level III | Swaptions (net)
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative assets, at fair value	0
Level III | Forward contracts (net)
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative assets, at fair value		0
Derivative liabilities, at fair value	0
Level III | Futures (net)
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative assets, at fair value	0
Derivative liabilities, at fair value		0
Level III | Corporate debt – bank debt
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Total investments	2,809,437	2,253,476
Level III | Corporate debt – all other
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Total investments	2,432,179	3,159,051
Level III | Equities – common stock
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Total investments	6,700,015	8,101,051
Level III | Equities – Preferred Stock
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Total investments	919,771	650,096
Level III | Equities – preferred stock
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Total investments	6,221,294	3,946,142
Level III | Real estate loan portfolio
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Total investments	2,369,441	1,737,822
Level III | Other
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Total investments	$ 13,708	$ 15,547