Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Schedule Of Deferred Income Tax Assets And Liabilities [Line Items]
Tax basis of loans in excess of financial statement basis	$ 12,534	$ 12,231
Minimum liability in defined benefit plan	4,502	3,954
Deferred compensation	2,002	1,807
Write-downs and adjustments to other real estate owned and repossessed assets	148	538
Other deferred tax assets	255	306
Total deferred tax assets	19,441	18,836
Financial statement basis of fixed assets in excess of tax basis	5,678	5,204
Intangible asset amortization deductible for tax purposes, but not for financial reporting purposes	8,992	7,761
Accretion on investment securities	1,563	2,129
Pension plan contributions	2,147	1,668
Net unrealized gain on investment securities Available-for-sale	32,130	29,383
Other deferred tax liabilities	389	433
Total deferred tax liabilities	50,899	46,578
Net deferred tax asset (liability)	$ (31,458)	$ (27,742)