Variable Interest Entities (Details Textual) (USD $)
6 Months Ended
Jun. 30, 2012
Dec. 31, 2011
Variable interest entities (Textual) [Abstract]    
Mortgage loans, carrying value $ 582,017,000 $ 604,772,000
Variable Interest Entities (Additional Textual) [Abstract]    
Maximum exposure to loss, required compliance period, years 15 years  
Real Estate Joint Ventures [Member]
   
Variable interest entities (Textual) [Abstract]    
Number of ventures invested by company 8 11
Affordable Housing Real Estate Joint Ventures [Member]
   
Variable interest entities (Textual) [Abstract]    
Number of ventures invested by company 28 28
Losses realizable if tax credits received were recaptured 11,200,000 13,200,000
Fixed-Rate Senior Mortgage Loan Commitments [Member]
   
Variable interest entities (Textual) [Abstract]    
Mortgage loans, carrying value $ 1,400,000 $ 6,400,000