Fair Value - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 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			$ 11,000	$ 11,000
Mutual fund securities transferred to Level 1					32,800,000
Credit loss included in noninterest income				161,000
Provision for loan losses expensed			3,900,000		4,000,000
Net carrying amount other real estate owned and other repossessed property					24,500,000
Other real estate owned property write-downs			2,100,000		15,300,000
Finance leases held for sale	11,553,000		11,553,000
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	105,000	34,000	206,000	65,000
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	21,600,000		21,600,000
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	32,500,000		32,500,000		34,100,000
Valuation allowance	$ 7,200,000		$ 7,200,000		$ 6,800,000