Indebtedness - Additional Information (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended				3 Months Ended		1 Months Ended								3 Months Ended				3 Months Ended				1 Months Ended	3 Months Ended							0 Months Ended	3 Months Ended					3 Months Ended					3 Months Ended				3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013	Mar. 31, 2014 Second Capped Call Option	Mar. 31, 2014 Second Capped Call Option Minimum	Mar. 31, 2014 Second Capped Call Option Maximum	Jan. 31, 2014 4.0% convertible senior notes Overallotment Option	Jan. 31, 2014 4.0% convertible senior notes Additional Principal Amount Overallotment Option Exercised By Underwriters	Mar. 31, 2014 CMBS Facilities	Dec. 31, 2013 CMBS Facilities	Mar. 31, 2014 Recourse Indebtedness		Dec. 31, 2013 Recourse Indebtedness		Mar. 31, 2014 Recourse Indebtedness 7.0% convertible senior notes		Dec. 31, 2013 Recourse Indebtedness 7.0% convertible senior notes		Mar. 31, 2014 Recourse Indebtedness 4.0% convertible senior notes		Dec. 31, 2013 Recourse Indebtedness 4.0% convertible senior notes		Jan. 31, 2014 Recourse Indebtedness Secured credit facilities	Mar. 31, 2014 Recourse Indebtedness Secured credit facilities	Dec. 31, 2013 Recourse Indebtedness Secured credit facilities	Mar. 31, 2014 Recourse Indebtedness CMBS Facilities	Dec. 31, 2013 Recourse Indebtedness CMBS Facilities	Mar. 31, 2014 Recourse Indebtedness CMBS Facilities $250,000 Thousand CMBS facility	Dec. 31, 2013 Recourse Indebtedness CMBS securitization	Mar. 31, 2014 Recourse Indebtedness CMBS securitization $150,000 Thousand Commercial Mortgage Facility	Jan. 27, 2014 Recourse Indebtedness CMBS securitization $75,000 Thousand Commercial Mortgage Facility	Mar. 31, 2014 Recourse Indebtedness CMBS securitization $75,000 Thousand Commercial Mortgage Facility	Mar. 31, 2014 Non-recourse indebtedness	Dec. 31, 2013 Non-recourse indebtedness	Mar. 31, 2014 Non-recourse indebtedness Loans payable on real estate	Dec. 31, 2013 Non-recourse indebtedness Loans payable on real estate	Mar. 31, 2014 Non-recourse indebtedness Loans payable on real estate First Mortgage MortgageLoan	Mar. 31, 2014 Non-recourse indebtedness CMBS securitization		Dec. 31, 2013 Non-recourse indebtedness CMBS securitization		Mar. 31, 2014 Non-recourse indebtedness CDO notes payable, at fair value		Dec. 31, 2013 Non-recourse indebtedness CDO notes payable, at fair value		Mar. 31, 2014 Non-recourse indebtedness CDO notes payable, at fair value re-directed from retained interests	Mar. 31, 2014 Non-recourse indebtedness CDO notes payable, at fair value Principal collections of the underlying collateral	Mar. 31, 2014 Non-recourse indebtedness CDO notes payable, at amortized cost		Dec. 31, 2013 Non-recourse indebtedness CDO notes payable, at amortized cost
Debt Instrument [Line Items]
Convertible note conversion rate															149.7815				99.2356
Principal amount of convertible note, conversion rate															$ 1				$ 1
Initial conversion price															$ 6.68				$ 10.08
Principal amount of convertible senior notes issued	84,000		86,000				16,750	141,750
Proceeds from issuance of convertible senior notes							16,300	137,238
Discount on convertible senior notes																			1,182
Cap price of capped call transaction				11.91
Initial strike price of capped call transaction				$ 9.57
Capped call expiration date					2018-06	2018-10
Revolving credit agreement term																								3 years
Outstanding borrowings																								2,500				22,133		26,373		50,578
LIBOR plus interest rate																								2.75%								2.00%
Payment of notes	6,777	7,502																					6,143															10,804				7,584				1,445	6,139
Line of credit facility, borrowing capacity																												250,000		150,000	75,000
Line of credit facility, remaining borrowing capacity																												227,867		123,627		24,422
Credit agreement term																															2 years
Principal amount repurchase convertible senior notes																																																5,800
Purchase price of notes																																																3,379
Gain on extinguishment of debt	2,421	0																																														2,421
Carrying Amount	2,257,238		2,086,401						1,652,296	1,662,537	307,176	[1]	235,011	[2]	33,058	[3]	32,938	[3]	132,419	[4]	116,184	[4]		5,000	11,129	22,133	30,618		7,131				1,950,062	1,851,390	299,548	171,244		89,331	[5]	100,139	[6]	399,448	[7],[8],[9]	377,235	[10],[7],[8]			1,161,735	[11],[7]	1,202,772	[12],[7]
Number of mortgages obtained																																					5
Unpaid Principal Balance	$ 2,730,710		$ 2,592,414								$ 323,671	[1]	$ 251,715	[2]	$ 34,066	[3]	$ 34,066	[3]	$ 141,750	[4]	$ 125,000	[4]		$ 5,000	$ 11,129	$ 22,133	$ 30,618		$ 7,131				$ 2,407,039	$ 2,340,699	$ 297,100	$ 171,244	$ 126,635	$ 89,331	[5]	$ 100,139	[6]	$ 857,616	[7],[8],[9]	$ 865,199	[10],[7],[8]			$ 1,162,992	[11],[7]	$ 1,204,117	[12],[7]
Contractual Maturity, start year																																					2016-04
Contractual Maturity, end year																																					2024-03
Stated interest rate, minimum																																					3.80%
Stated interest rate, maximum																																					5.60%

[1] Excludes senior secured notes issued by us with an aggregate principal amount equal to $84,000 with a weighted average coupon of 7.0%, which are eliminated in consolidation.

[2] Excludes senior secured notes issued by us with an aggregate principal amount equal to $86,000 with a weighted average coupon of 7.0%, which are eliminated in consolidation.

[3] Our 7.0% convertible senior notes are redeemable at par, at the option of the holder, in April 2016, April 2021, and April 2026.

[4] Our 4.0% convertible senior notes are redeemable at par, at the option of the holder, in October 2018, October 2023, and October 2028.

[5] Excludes the FL1 junior notes purchased by us which are eliminated in consolidation. Collateralized by $123,093 principal amount of commercial mortgages loans and participation interests. These obligations were issued by separate legal entities and consequently the assets of the special purpose entities that collateralize these obligations are not available to our creditors.

[6] Excludes the FL1 junior notes purchased by us which are eliminated in consolidation. Collateralized by $131,843 principal amount of commercial mortgages loans and participation interests. These obligations were issued by separate legal entities and consequently the assets of the special purpose entities that collateralize these obligations are not available to our creditors.

[7] Excludes CDO notes payable purchased by us which are eliminated in consolidation.

[8] Relates to liabilities which we elected to record at fair value under FASB ASC Topic 825.

[9] Collateralized by $983,429 principal amount of investments in securities and security-related receivables and loans, before fair value adjustments. The fair value of these investments as of March 31, 2014 was $741,732. These obligations were issued by separate legal entities and consequently the assets of the special purpose entities that collateralize these obligations are not available to our creditors.

[10] Collateralized by $989,781 principal amount of investments in securities and security-related receivables and loans, before fair value adjustments. The fair value of these investments as of December 31, 2013 was $746,939. These obligations were issued by separate legal entities and consequently the assets of the special purpose entities that collateralize these obligations are not available to our creditors.

[11] Collateralized by $1,652,296 principal amount of commercial mortgages, mezzanine loans, other loans and preferred equity interests. These obligations were issued by separate legal entities and consequently the assets of the special purpose entities that collateralize these obligations are not available to our creditors.

[12] Collateralized by $1,662,537 principal amount of commercial mortgages, mezzanine loans, other loans and preferred equity interests. These obligations were issued by separate legal entities and consequently the assets of the special purpose entities that collateralize these obligations are not available to our creditors.