CRE Debt and Preferred Equity Investments (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013
Transaction to Real Estate Investments [Line Items]
Carrying Value	$ 1,640,206		$ 1,583,969
Commercial Mortgage
Transaction to Real Estate Investments [Line Items]
Outstanding Principal	1,644,373		1,587,223
Carrying Value	1,640,206	[1]	1,583,969	[1]
Percentage of Loan Portfolio	100.00%	[2]	100.00%	[2]
Commercial Mortgage | Senior Mortgages
Transaction to Real Estate Investments [Line Items]
Outstanding Principal	337,845		669,512
Carrying Value	336,845	[1]	667,299	[1]
Percentage of Loan Portfolio	20.50%	[2]	42.20%	[2]
Commercial Mortgage | Senior Securitized Mortgages
Transaction to Real Estate Investments [Line Items]
Outstanding Principal	399,541	[3]
Carrying Value	398,113	[1],[3],[4]
Percentage of Loan Portfolio	24.30%	[2],[3]	0.00%	[2],[3]
Commercial Mortgage | Subordinated Notes
Transaction to Real Estate Investments [Line Items]
Outstanding Principal	15,965		41,059
Carrying Value	16,049	[1]	41,408	[1]
Percentage of Loan Portfolio	1.00%	[2]	2.60%	[2]
Commercial Mortgage | Mezzanine Loans
Transaction to Real Estate Investments [Line Items]
Outstanding Principal	641,253		626,883
Carrying Value	641,887	[1]	628,102	[1]
Percentage of Loan Portfolio	39.00%	[2]	39.50%	[2]
Commercial Mortgage | Preferred Equity Interests
Transaction to Real Estate Investments [Line Items]
Outstanding Principal	249,769		249,769
Carrying Value	$ 247,312	[1]	$ 247,160	[1]
Percentage of Loan Portfolio	15.20%	[2]	15.70%	[2]

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

[2] (2) Based on outstanding principal.

[3] (3) Assets of consolidated VIE.

[4] (1) Assets of consolidated VIE.