Fair Value - Additional Information (Detail) (USD $)	3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 30, 2013	Jun. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Accretion of discounts on securities included in interest income				$ 16,000	$ 18,000
Mutual fund securities transferred to Level 1						32,800,000
Credit loss included in noninterest income					165,000
Provision for loan losses expensed				3,100,000		4,000,000
Net carrying amount other real estate owned and other repossessed property						24,500,000
Other real estate owned property write-downs				2,600,000		15,300,000
Finance leases held for sale		11,600,000
Loss recognized due to transfer of leases		200,000
Past due period of mortgage loans held for sale, days				90 days
Interest income for residential loans held for sale	91,000		44,000	297,000	109,000
Valuation Allowance, Real Estate Owned [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Net carrying amount other real estate owned and other repossessed property	14,100,000			14,100,000
Minimum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Appraisals discount rate				0.00%
Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Appraisals discount rate				45.00%
Impaired Commercial and Commercial Real Estate Loans [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Principal amount of impaired commercial and commercial real estate loans	19,800,000			19,800,000		34,100,000
Valuation allowance	$ 6,500,000			$ 6,500,000		$ 6,800,000