FAIR VALUE - Summary of Changes in Fair Value of Level III Investments (Detail) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013 Corporate debt-bank debt [Member]	Mar. 31, 2012 Corporate debt-bank debt [Member]	Mar. 31, 2013 Corporate debt-all other [Member]	Mar. 31, 2012 Corporate debt-all other [Member]	Mar. 31, 2013 Equities - common stock [Member]	Mar. 31, 2012 Equities - common stock [Member]	Mar. 31, 2013 Equities-preferred stock [Member]	Mar. 31, 2012 Equities-preferred stock [Member]	Mar. 31, 2013 Real estate [Member]	Mar. 31, 2012 Real estate [Member]	Mar. 31, 2013 Other [Member]	Mar. 31, 2012 Other [Member]	Mar. 31, 2013 Real Estate Loan Portfolio [Member]	Mar. 31, 2012 Real Estate Loan Portfolio [Member]	Mar. 31, 2013 Swap [Member]	Mar. 31, 2012 Swap [Member]	Mar. 31, 2013 Level III [Member]	Dec. 31, 2012 Level III [Member]	Mar. 31, 2013 Swaps (net)-corporate debt [Member] Level II [Member]	Dec. 31, 2012 Swaps (net)-corporate debt [Member] Level II [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Transfers between Level I and Level II	$ 1,066,800,000
Fair Value of Debt Obligations																			651,100,000	652,900,000
Beginning balance	19,907,890,000	15,673,386,000	2,253,476,000	1,978,637,000	3,159,051,000	3,155,241,000	8,101,051,000	6,164,025,000	650,096,000	1,090,107,000	3,946,142,000	2,786,862,000	15,547,000	18,824,000	1,737,822,000	479,690,000	44,705,000	0
Transfers into Level III	709,646,000	818,544,000	49,731,000	307,574,000	6,131,000	327,640,000	528,314,000	178,104,000	125,470,000	5,226,000	0	0	0	0	0	0	0	0
Transfers out of Level III	(690,463,000)	(597,779,000)	(193,810,000)	(33,231,000)	(97,875,000)	(119,410,000)	(398,778,000)	(351,594,000)	0	(88,191,000)	0	(5,353,000)	0	0	0	0	0	0
Purchases	780,456,000	1,119,516,000	134,839,000	514,000,000	33,584,000	118,573,000	51,039,000	183,328,000	29,300,000	11,452,000	307,269,000	133,889,000	0	0	224,425,000	158,274,000	0	0
Sales	(1,997,931,000)	(131,917,000)	(183,236,000)	(30,389,000)	(198,596,000)	(10,829,000)	(1,127,763,000)	(56,634,000)	(178,320,000)	(446,000)	(26,834,000)	(8,655,000)	0	0	(283,182,000)	(24,964,000)	0	0
Realized gains (losses), net	459,561,000	(21,589,000)	(17,014,000)	383,000	23,255,000	5,223,000	426,537,000	(28,326,000)	29,034,000	(4,188,000)	(9,325,000)	(136,000)	0	0	7,074,000	5,455,000	0	0
Unrealized appreciation (depreciation), net	6,269,000	540,513,000	23,452,000	(16,617,000)	(12,712,000)	94,531,000	(332,554,000)	270,427,000	(7,748,000)	42,810,000	281,674,000	149,347,000	(57,000)	15,000	44,245,000	0	9,969,000	0
Ending balance	19,175,428,000	17,400,674,000	2,067,438,000	2,720,357,000	2,912,838,000	3,570,969,000	7,247,846,000	6,359,330,000	647,832,000	1,056,770,000	4,498,926,000	3,055,954,000	15,490,000	18,839,000	1,730,384,000	618,455,000	54,674,000	0
Net change in unrealized appreciation (depreciation) attributable to asset still held at end of period	572,586,000	281,440,000	33,359,000	(125,075,000)	27,735,000	111,646,000	145,621,000	111,589,000	32,491,000	38,935,000	279,223,000	144,330,000	(58,000)	15,000	44,245,000	0	9,970,000	0
Average borrowing rates																			3.10%	3.10%
Percentage increase in average borrowing rate assumption that would lower fair value of debt obligation																			10.00%
Fair value of debt obligation, decrease in value due to increase in average borrowing rate																			644,300,000
Percentage decrease in average borrowing rate assumption that would increase fair value of debt obligation																			10.00%
Fair value of debt obligation, increase in value due to decrease in average borrowing rate																			659,700,000
Accounts payable, other accrued expenses and other liabilities																					$ 7,400,000	$ 7,900,000