Internal CRE Debt and Preferred Equity Ratings (Detail) - Commercial Mortgage - USD ($) $ in Thousands		Sep. 30, 2015		Dec. 31, 2014
Transaction to Real Estate Investments [Line Items]
Performing Loans		$ 1,298,757		$ 1,498,749
Internal Ratings Watch List		9,250		9,250
Defaulted-Recovery		12,973	[1]	12,973	[2]
Impaired		0		0
Senior Mortgages
Transaction to Real Estate Investments [Line Items]
Performing Loans		309,591		371,331
Defaulted-Recovery		12,973	[1]	12,973	[2]
Impaired		0		0
Senior Securitized Mortgages
Transaction to Real Estate Investments [Line Items]
Performing Loans	[2]	305,922		390,291
Internal Ratings Watch List	[2]	9,250		9,250
Impaired	[2]	0		0
Preferred Equity Interests
Transaction to Real Estate Investments [Line Items]
Performing Loans		122,444		214,653
Impaired		0		0
Mezzanine Loans
Transaction to Real Estate Investments [Line Items]
Performing Loans		560,800		522,474
Impaired		$ 0		$ 0

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

[2] Assets of consolidated VIE.