CRE Debt and Preferred Equity Investments (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013
Transaction to Real Estate Investments [Line Items]
Net investment in commercial mortgage loans and preferred equity	$ 1,227,182
Carrying Value	1,231,203
Commercial Mortgage
Transaction to Real Estate Investments [Line Items]
Net origination fees	(4,021)
Outstanding Principal	1,229,297
Carrying Value	1,231,203
Percentage of Loan Portfolio	100.00%	[1]
Commercial Mortgage | Senior Mortgages
Transaction to Real Estate Investments [Line Items]
Outstanding Principal	431,000
Carrying Value	431,472
Percentage of Loan Portfolio	35.10%	[1]
Commercial Mortgage | Subordinated Notes
Transaction to Real Estate Investments [Line Items]
Outstanding Principal	41,149
Carrying Value	41,571
Percentage of Loan Portfolio	3.30%	[1]
Commercial Mortgage | Mezzanine Loans
Transaction to Real Estate Investments [Line Items]
Outstanding Principal	567,379
Carrying Value	569,045
Percentage of Loan Portfolio	46.20%	[1]
Commercial Mortgage | Preferred Equity Interests
Transaction to Real Estate Investments [Line Items]
Outstanding Principal	189,769
Carrying Value	$ 189,115
Percentage of Loan Portfolio	15.40%	[1]

[1] Based on outstanding principal.