BORROWINGS (Details) (USD $)							3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended					3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended					3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended		12 Months Ended	3 Months Ended	12 Months Ended					3 Months Ended	12 Months Ended					3 Months Ended	12 Months Ended	3 Months Ended		12 Months Ended			3 Months Ended			12 Months Ended		3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 Affiliates	Dec. 31, 2012 Affiliates	Mar. 31, 2013 Nonaffiliates	Dec. 31, 2012 Nonaffiliates	Mar. 31, 2013 CLO 2005-1 senior secured notes	Dec. 31, 2012 CLO 2005-1 senior secured notes	Mar. 31, 2013 CLO 2005-2 senior secured notes	Dec. 31, 2012 CLO 2005-2 senior secured notes	Mar. 31, 2013 CLO 2006-1 senior secured notes	Dec. 31, 2012 CLO 2006-1 senior secured notes	Mar. 31, 2013 CLO 2007-1 senior secured notes	Dec. 31, 2012 CLO 2007-1 senior secured notes	Mar. 31, 2013 CLO 2007-1 junior secured notes Nonaffiliates	Dec. 31, 2012 CLO 2007-1 junior secured notes Nonaffiliates	Mar. 31, 2013 CLO 2007-1 junior secured mezzanine notes Nonaffiliates	Dec. 31, 2012 CLO 2007-1 junior secured mezzanine notes Nonaffiliates	Mar. 31, 2013 CLO 2007-1 junior secured subordinated notes Nonaffiliates	Dec. 31, 2012 CLO 2007-1 junior secured subordinated notes Nonaffiliates	Mar. 31, 2013 CLO 2007-A senior secured notes	Dec. 31, 2012 CLO 2007-A senior secured notes	Mar. 31, 2013 CLO 2007-A junior secured notes Nonaffiliates	Dec. 31, 2012 CLO 2007-A junior secured notes Nonaffiliates	Mar. 31, 2013 CLO 2007-A junior secured mezzanine notes Nonaffiliates	Dec. 31, 2012 CLO 2007-A junior secured mezzanine notes Nonaffiliates	Mar. 31, 2013 CLO 2007-A junior secured subordinated notes Nonaffiliates	Dec. 31, 2012 CLO 2007-A junior secured subordinated notes Nonaffiliates	Mar. 31, 2013 CLO 2011-1 senior debt	Dec. 31, 2012 CLO 2011-1 senior debt	Mar. 31, 2013 CLO 2012-1 senior secured notes	Dec. 31, 2012 CLO 2012-1 senior secured notes	Mar. 31, 2013 CLO 2012-1 senior secured notes Nonaffiliates	Mar. 31, 2013 CLO 2012-1 junior secured notes	Dec. 31, 2012 CLO 2012-1 junior secured notes	Mar. 31, 2013 CLO 2007-1 junior secured notes to affiliates Affiliates	Dec. 31, 2012 CLO 2007-1 junior secured notes to affiliates Affiliates	Mar. 31, 2013 CLO 2007-1 junior secured mezzanine notes to affiliates Affiliates	Dec. 31, 2012 CLO 2007-1 junior secured mezzanine notes to affiliates Affiliates	Mar. 31, 2013 CLO 2007-1 junior secured subordinated notes to affiliates Affiliates	Dec. 31, 2012 CLO 2007-1 junior secured subordinated notes to affiliates Affiliates	Mar. 31, 2013 CLO 2007-A junior secured notes to affiliates Affiliates	Dec. 31, 2012 CLO 2007-A junior secured notes to affiliates Affiliates	Mar. 31, 2013 CLO 2007-A junior secured mezzanine notes to affiliates Affiliates	Dec. 31, 2012 CLO 2007-A junior secured mezzanine notes to affiliates Affiliates	Mar. 31, 2013 CLO 2007-A junior secured subordinated notes to affiliates Affiliates	Dec. 31, 2012 CLO 2007-A junior secured subordinated notes to affiliates Affiliates	Mar. 31, 2013 2015 Facility	Dec. 31, 2012 2015 Facility	Mar. 31, 2013 2015 Facility LIBOR	Mar. 31, 2013 2015 Natural Resources Facility	Dec. 31, 2012 2015 Natural Resources Facility	Mar. 31, 2013 2015 Natural Resources Facility Minimum LIBOR	Mar. 31, 2013 2015 Natural Resources Facility Maximum LIBOR	Mar. 31, 2013 2018 Natural Resources Facility	Mar. 31, 2013 2018 Natural Resources Facility Minimum LIBOR	Mar. 31, 2013 2018 Natural Resources Facility Maximum LIBOR	Dec. 31, 2012 7 500% convertible senior notes	Jan. 18, 2013 7 500% convertible senior notes	Mar. 31, 2013 8 375% Senior Notes due November 15, 2041	Dec. 31, 2012 8 375% Senior Notes due November 15, 2041	Mar. 31, 2013 7 500% Senior notes due March 20, 2042	Dec. 31, 2012 7 500% Senior notes due March 20, 2042	Mar. 31, 2013 Junior subordinated notes	Dec. 31, 2012 Junior subordinated notes
Details of Company's borrowings
Collateralized loan obligation secured debt			$ 193,921,000	$ 296,557,000	$ 5,058,520,000	$ 5,122,338,000	$ 374,482,000	$ 427,317,000	$ 432,932,000	$ 470,516,000	$ 566,661,000	$ 601,091,000	$ 2,075,040,000	$ 2,075,040,000	$ 296,925,000	$ 209,555,000	$ 291,100,000	$ 203,700,000	$ 5,800,000	$ 5,800,000	$ 580,409,000	$ 601,375,000	$ 26,164,000	$ 10,179,000	$ 21,600,000	$ 5,600,000	$ 4,600,000	$ 4,600,000	$ 322,020,000	$ 343,485,000	$ 362,387,000	$ 362,280,000		$ 21,500,000	$ 21,500,000	$ 162,430,000	$ 249,115,000	$ 32,100,000	$ 118,800,000	$ 130,300,000	$ 130,300,000	$ 31,491,000	$ 47,442,000	$ 21,000,000	$ 36,900,000	$ 10,500,000	$ 10,500,000
Senior notes	362,202,000	362,178,000																																																										250,751,000	250,735,000	111,451,000	111,443,000
Credit facilities	46,089,000	107,789,000																																																	46,089,000	107,789,000			0
Convertible senior notes		166,028,000																																																								166,028,000	172,500,000
Junior subordinated notes	283,517,000	283,517,000																																																														283,517,000	283,517,000
Total borrowings	5,944,249,000	6,338,407,000																																																								166,000,000
Weighted Average Borrowing Rate (as a percent)							0.69%	0.69%	0.65%	0.66%	0.68%	0.69%	0.84%	0.86%			3.40%	2.80%			1.48%	1.50%			7.10%	7.00%			1.65%	1.67%	2.58%	2.58%						9.80%	6.30%					7.80%	7.50%			2.53%	2.56%		2.20%	2.71%						7.50%		8.38%	8.38%	7.50%	7.50%	5.42%	5.43%
Weighted Average Remaining Maturity							1487 days	1577 days	1701 days	1791 days	1973 days	2063 days	2967 days	3057 days	2967 days	3057 days					1659 days	1749 days	1659 days	1749 days					1963 days	2053 days	4277 days	4367 days		4277 days	4367 days	2967 days	3057 days					1659 days	1749 days					974 days	1064 days		949 days	1039 days			1794 days			1476 days		10456 days	10546 days	10581 days	10671 days	8622 days	8712 days
Collateralized loan obligation secured debt, fair value of collateral			217,574,000	331,037,000	5,847,264,000	5,679,542,000	405,834,000	510,187,000	565,936,000	618,000,000	803,977,000	846,365,000	2,310,115,000	2,298,373,000	330,562,000	232,109,000					677,212,000	698,569,000	30,527,000	11,824,000					401,169,000	421,584,000	304,139,000	40,180,000		17,793,000	2,351,000	180,831,000	275,927,000					36,743,000	55,110,000
Credit facilities, fair value of collateral	224,378,000	227,415,000																																																	224,378,000	227,415,000
Fair Value of Collateral	6,289,216,000	6,237,994,000
Percentage of margin added to reference rate to determine interest rate on debt																																	2.09%																	2.25%			1.75%	2.75%		1.75%	2.75%
Principal cash held																																$ 357,700,000
Debt, variable interest rate basis																																	three-month LIBOR																	LIBOR	LIBOR				LIBOR