Impaired Loans and Valuation Allowance for Loan Losses - Additional Information (Detail) (USD $)	3 Months Ended			9 Months Ended
	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Financing Receivable, Modifications [Line Items]
Newly identified TDRs	$ 1,700,000	$ 4,100,000	$ 4,400,000	$ 10,200,000
Loan default period				60 days
Accruing TDRs	25,500,000			25,500,000		41,900,000
Interest income on impaired loans				910,000	2,400,000
Expected future cash flows of impaired loans				1,069,000	759,000
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Newly identified TDRs				3,400,000
Residential Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Newly identified TDRs				1,000,000
Consumer [Member]
Financing Receivable, Modifications [Line Items]
Newly identified TDRs				$ 100,000