Federal Funds and Overnight Funds Purchased - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Unsecured federal funds borrowing lines	$ 113,000
Unsecured federal funds borrowing lines outstanding	11,570	12,300
Secured overnight borrowing line from Federal Reserve Bank	87,740
Commercial loans pledged for Federal Reserve Bank borrowing line	131,196
Outstanding borrowings	$ 0	$ 0