Internal CRE Debt and Preferred Equity Ratings (Detail) (Commercial Mortgage, USD $) In Thousands, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Transaction to Real Estate Investments [Line Items]
Performing Loans	$ 1,199,028		$ 1,498,749
Internal Ratings Watch List	290,250	[1]	9,250
Defaulted-Recovery	12,973	[2]	12,973
Impaired	0		0
Senior Mortgages
Transaction to Real Estate Investments [Line Items]
Performing Loans	188,899		371,331
Internal Ratings Watch List	230,000	[1]
Defaulted-Recovery	12,973	[2]	12,973	[2]
Impaired	0		0
Senior Securitized Mortgages
Transaction to Real Estate Investments [Line Items]
Performing Loans	352,611	[3]	390,291	[3]
Internal Ratings Watch List	9,250	[1],[3]	9,250	[3]
Impaired	0	[3]	0	[3]
Subordinated Notes
Transaction to Real Estate Investments [Line Items]
Impaired			0
Preferred Equity Interests
Transaction to Real Estate Investments [Line Items]
Performing Loans	162,213		214,653
Internal Ratings Watch List	51,000	[1]
Impaired	0		0
Mezzanine Loans
Transaction to Real Estate Investments [Line Items]
Performing Loans	495,305		522,474
Impaired	$ 0		$ 0

[1] Includes a $230.0 million loan maturing on June 30, 2015 with a risk that the borrower will be unable to refinance the outstanding principal amount before the maturity date, but full recovery is expected.

[2] Related to one loan on non-accrual status.

[3] Assets of consolidated VIE.