CRE Debt and Preferred Equity Investments -Based on Outstanding Principal (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2014		Dec. 31, 2013
Transaction to Real Estate Investments [Line Items]
Beginning balance	$ 1,583,969		$ 1,227,182
Originations & advances (principal)	126,946		436,190
Principal payments	(69,796)		(64,513)
Sales (principal)			(13,750)
Amortization & accretion of (premium) discounts	(890)
Amortization & accretion of (premium) discounts	792		(271)
Net (increase) decrease in origination fees	(996)		(1,693)
Amortization of net origination fees	973
Amortization of net origination fees	(973)		824
Allowance for loan losses
Net carrying value	1,640,206		1,583,969
Commercial Mortgage
Transaction to Real Estate Investments [Line Items]
Net carrying value	1,640,206	[1]	1,583,969	[1]
Commercial Mortgage | Senior Mortgages
Transaction to Real Estate Investments [Line Items]
Beginning balance	667,299		429,229
Originations & advances (principal)	67,946		240,150
Principal payments	(72)		(388)
Sales (principal)			(13,750)
Amortization & accretion of (premium) discounts	(36)
Amortization & accretion of (premium) discounts			(37)
Net (increase) decrease in origination fees	(1,012)		(1,106)
Amortization of net origination fees	698
Amortization of net origination fees			701
Transfers	(397,978)		12,500
Allowance for loan losses
Net carrying value	336,845	[1]	667,299	[1]
Commercial Mortgage | Senior Securitized Mortgages
Transaction to Real Estate Investments [Line Items]
Amortization of net origination fees	135	[2]
Transfers	397,978	[2]
Allowance for loan losses		[2]		[2]
Net carrying value	398,113	[1],[2],[3]
Commercial Mortgage | Subordinated Notes
Transaction to Real Estate Investments [Line Items]
Beginning balance	41,408		41,571
Principal payments	(25,094)		(90)
Amortization & accretion of (premium) discounts	(265)
Amortization & accretion of (premium) discounts			(73)
Allowance for loan losses
Net carrying value	16,049	[1]	41,408	[1]
Commercial Mortgage | Mezzanine Loans
Transaction to Real Estate Investments [Line Items]
Beginning balance	628,102		568,759
Originations & advances (principal)	59,000		136,040
Principal payments	(44,630)		(64,035)
Amortization & accretion of (premium) discounts	(617)
Amortization & accretion of (premium) discounts			(192)
Net (increase) decrease in origination fees	15		14
Amortization of net origination fees	17
Amortization of net origination fees			16
Transfers			(12,500)
Allowance for loan losses
Net carrying value	641,887	[1]	628,102	[1]
Commercial Mortgage | Preferred Equity Interests
Transaction to Real Estate Investments [Line Items]
Beginning balance	247,160		187,623
Originations & advances (principal)			60,000
Amortization & accretion of (premium) discounts	28
Amortization & accretion of (premium) discounts			31
Net (increase) decrease in origination fees	1		(601)
Amortization of net origination fees	123
Amortization of net origination fees			107
Allowance for loan losses
Net carrying value	$ 247,312	[1]	$ 247,160	[1]

[1] (1) Net carrying value includes unamortized origination fees of $4.9 million.

[2] (1) Assets of consolidated VIE.

[3] (3) Assets of consolidated VIE.