Commitments - Financial Instrument Whose Contract Amounts Represent Credit Risk (Detail) (USD $)
Dec. 31, 2014
Dec. 31, 2013
Commitments to Extend Credit [Member]    
Product Royalty Future Minimum Payment Due [Line Items]    
Commitments to extend credit $ 182,820,000 $ 141,887,000
Standby Letters of Credit [Member]    
Product Royalty Future Minimum Payment Due [Line Items]    
Stand-by letters of credit $ 8,085,000 $ 4,066,000