Fair Value of Financial Instruments (Details) (USD $)	3 Months Ended	9 Months Ended
	Sep. 30, 2011	Sep. 30, 2011	Jun. 30, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Dec. 31, 2009
Financial Assets:
Securities available-for-sale	$ 786,195,000	$ 786,195,000		$ 838,894,000
Corporate loans, allowance for loan losses (in dollars)	191,407,000	191,407,000	188,874,000	209,030,000	209,030,000	210,218,000	237,308,000
Residential mortgage-backed securities, at estimated fair value	88,209,000	88,209,000		93,929,000
Equity investments, at estimated fair value	170,175,000	170,175,000		99,955,000
Derivative assets	26,066,000	26,066,000		19,519,000
Financial Liabilities:
Collateralized loan obligation secured debt	5,596,020,000	5,596,020,000		5,630,272,000
Convertible senior notes	299,877,000	299,877,000		344,142,000
Junior subordinated notes	283,517,000	283,517,000		283,517,000
Accounts payable, accrued expenses and other liabilities	52,596,000	52,596,000		14,193,000
Accrued interest payable	15,987,000	15,987,000		22,846,000
Related party payable	3,687,000	3,687,000		12,988,000
Other-than-temporary impairment on private equity investments	0	1,100,000
Affiliates | Carrying Amount
Financial Liabilities:
Collateralized loan obligation secured debt	365,848,000	365,848,000		366,124,000
Accrued interest payable	7,579,000	7,579,000		6,316,000
Carrying Amount
Financial Assets:
Cash, restricted cash, and cash equivalents	459,043,000	459,043,000		885,254,000
Securities available-for-sale	786,195,000	786,195,000		838,894,000
Corporate loans, net of allowance for loan losses of $191,407 and $209,030 as of September 30, 2011 and December 31, 2010 respectively	6,115,948,000	6,115,948,000		5,857,816,000
Corporate loans, allowance for loan losses (in dollars)	191,407,000	191,407,000		209,030,000
Corporate loans held for sale	500,490,000	500,490,000		463,628,000
Residential mortgage-backed securities, at estimated fair value	88,209,000	88,209,000		93,929,000
Equity investments, at estimated fair value	170,175,000	170,175,000		99,955,000
Interest and principal receivable	59,917,000	59,917,000		57,414,000
Derivative assets	26,066,000	26,066,000		19,519,000
Private equity investments, at cost	3,672,000	3,672,000		4,800,000
Financial Liabilities:
Collateralized loan obligation secured debt	5,596,020,000	5,596,020,000		5,630,272,000
Credit facilities	38,300,000	38,300,000		18,400,000
Convertible senior notes	299,877,000	299,877,000		344,142,000
Junior subordinated notes	283,517,000	283,517,000		283,517,000
Accounts payable, accrued expenses and other liabilities	51,404,000	51,404,000		14,193,000
Accrued interest payable	15,987,000	15,987,000		22,846,000
Related party payable	3,687,000	3,687,000		12,988,000
Securities sold, not yet purchased	1,192,000	1,192,000
Derivative liabilities	123,957,000	123,957,000		76,566,000
Affiliates | Estimated Fair Value
Financial Liabilities:
Collateralized loan obligation secured debt	288,913,000	288,913,000		254,522,000
Accrued interest payable	7,579,000	7,579,000		6,316,000
Estimated Fair Value
Financial Assets:
Cash, restricted cash, and cash equivalents	459,043,000	459,043,000		885,254,000
Securities available-for-sale	786,195,000	786,195,000		838,894,000
Corporate loans, net of allowance for loan losses of $191,407 and $209,030 as of September 30, 2011 and December 31, 2010 respectively	5,904,793,000	5,904,793,000		6,060,530,000
Corporate loans, allowance for loan losses (in dollars)	191,407,000	191,407,000		209,030,000
Corporate loans held for sale	537,112,000	537,112,000		473,681,000
Residential mortgage-backed securities, at estimated fair value	88,209,000	88,209,000		93,929,000
Equity investments, at estimated fair value	170,175,000	170,175,000		99,955,000
Interest and principal receivable	59,917,000	59,917,000		57,414,000
Derivative assets	26,066,000	26,066,000		19,519,000
Private equity investments, at cost	1,675,000	1,675,000		5,051,000
Financial Liabilities:
Collateralized loan obligation secured debt	5,248,045,000	5,248,045,000		5,176,052,000
Credit facilities	38,300,000	38,300,000		18,400,000
Convertible senior notes	356,203,000	356,203,000		425,564,000
Junior subordinated notes	263,671,000	263,671,000		264,025,000
Accounts payable, accrued expenses and other liabilities	51,404,000	51,404,000		14,193,000
Accrued interest payable	15,987,000	15,987,000		22,846,000
Related party payable	3,687,000	3,687,000		12,988,000
Securities sold, not yet purchased	1,192,000	1,192,000
Derivative liabilities	123,957,000	123,957,000		76,566,000
Affiliates
Financial Liabilities:
Collateralized loan obligation secured debt	365,848,000	365,848,000		366,124,000
Accrued interest payable	7,579,000	7,579,000		6,316,000
Non-affiliates
Financial Liabilities:
Collateralized loan obligation secured debt	$ 5,600,000,000	$ 5,600,000,000		$ 5,600,000,000