Business Combinations - Summary of Changes in Carrying Amount of Accretable Yield on Acquired Loans (Detail) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 15, 2014
Business Combination Increase Decrease To Reflect Liabilities Acquired At Fair Value [Abstract]    
Acquisition of United $ 1,480 $ 9,027
Accretion (13)  
Net transfers from non-accretable difference to accretable yield 0  
Balance, end of year $ 1,467