Carrying Amount and Maximum Exposure to Loss Relating to VIEs (Detail) (USD $)
In Thousands, unless otherwise specified
Sep. 30, 2012
Dec. 31, 2011
Variable Interest Entity [Line Items]    
Carrying Amount $ 47,123 $ 56,300
Maximum Exposure to Loss 84,452 96,675
Real Estate Joint Ventures
   
Variable Interest Entity [Line Items]    
Carrying Amount 24,033 35,551
Maximum Exposure to Loss 24,033 35,551
Affordable Housing Real Estate Joint Ventures
   
Variable Interest Entity [Line Items]    
Carrying Amount 23,090 20,749
Maximum Exposure to Loss $ 60,419 $ 61,124