Gross Mortgage Loan Principal Outstanding and Allowance for Potential Future Losses (Detail) (USD $)
In Thousands, unless otherwise specified
Sep. 30, 2012
Jun. 30, 2012
Dec. 31, 2011
Mortgage Loans on Real Estate [Line Items]      
Principal outstanding $ 563,214 $ 563,214 $ 604,772
Allowance for potential future losses (2,442)   (2,849)
Carrying value $ 560,772   $ 601,923