CRE Debt and Preferred Equity Investments (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Transaction to Real Estate Investments [Line Items]
Carrying Value	$ 1,498,406		$ 1,518,165
Preferred Equity Interests
Transaction to Real Estate Investments [Line Items]
Carrying Value	211,594		212,905
Commercial Mortgage
Transaction to Real Estate Investments [Line Items]
Outstanding Principal	1,502,251		1,520,972
Carrying Value	1,498,406	[1]	1,518,165	[1]
Percentage of Loan Portfolio	100.00%	[2]	100.00%	[2]
Commercial Mortgage | Senior Mortgages
Transaction to Real Estate Investments [Line Items]
Outstanding Principal	431,872		384,304
Carrying Value	430,228	[1],[3]	383,895	[1]
Percentage of Loan Portfolio	28.70%	[2]	25.20%	[2]
Commercial Mortgage | Senior Securitized Mortgages
Transaction to Real Estate Investments [Line Items]
Outstanding Principal	361,861	[3]	399,541	[3]
Carrying Value	361,179	[1],[3]	398,634	[1],[3]
Percentage of Loan Portfolio	24.10%	[2],[3]	26.30%	[2],[3]
Commercial Mortgage | Preferred Equity Interests
Transaction to Real Estate Investments [Line Items]
Outstanding Principal	213,213		214,653
Carrying Value	211,594	[1]	212,905	[1]
Percentage of Loan Portfolio	14.20%	[2]	14.10%	[2]
Commercial Mortgage | Mezzanine Loans
Transaction to Real Estate Investments [Line Items]
Outstanding Principal	495,305		522,474
Carrying Value	$ 495,405	[1]	$ 522,731	[1]
Percentage of Loan Portfolio	33.00%	[2]	34.40%	[2]

[1] Carrying value includes unamortized origination fees of $4.4 million and $3.0 million as of March 31, 2015 and December 31, 2014, respectively.

[2] Based on outstanding principal.

[3] Assets of consolidated VIE.