Short-Term Borrowings - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Short-term Debt [Line Items]
Line of credit	50.00%
Home equity lines of credit	$ 85,929
Available line of credit	42,965
Outstanding amount	0	0
Line of credit with an unaffiliated financial institution	4,000
Balance line of credit	0	0
Securities sold under repurchase agreements	988	227
Interest rate paid on borrowings	0.15%	0.15%
Federal funds purchased	$ 0	$ 0