Restrictions on Cash and Due from Banks and Interest-earning Deposit Accounts - Additional Information (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Cash and Cash Equivalents [Abstract]
Reserve requirement at Federal Reserve Bank	$ 2,500,000	$ 8,300,000
Average balances at Federal Reserve Bank	31,500,000	44,500,000
Interest-earning deposit accounts pledged for Risk Participation Agreements	$ 370,000	$ 690,000