Outstanding Principal Balance and Carrying Amount of Loans Included in Consolidated Balance Sheet (Detail) (USD $)
In Thousands, unless otherwise specified
Sep. 30, 2012
Dec. 31, 2011
Business Acquisition [Line Items]    
Outstanding principal balance $ 26,467 $ 385,152
Carrying amount 26,099  
Business acquisition
   
Business Acquisition [Line Items]    
Outstanding principal balance 26,467  
Carrying amount $ 26,099