Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Deferred Tax Assets, Gross [Abstract]
Allowance for credit losses	$ 18,979	$ 23,515
Postretirement benefits other than pensions	726	769
Alternative minimum tax credit carryforward	13,896	13,026
Unrealized loss on securities available for sale	11,235	0
Writedown of other real estate owned	207	3,647
Deferred compensation	2,118	2,203
Accrued interest on nonaccrual loans	1,481	3,887
Other-than-temporary impairment of securities	9,693	15,233
Depreciation of assets	1,546	952
Accrued incentives	1,153	0
Unfunded loan commitment allowance	1,106	836
Deferred rent	653	0
Other	2,462	2,795
Total deferred tax assets	65,255	66,863
Deferred tax liabilities:
Basis difference in assets acquired	(518)	(808)
Loan origination fees and costs	(637)	(606)
Income from unconsolidated subsidiary	(590)	(575)
Unrealized gain on securities available for sale	0	(592)
Other	(332)	(150)
Total deferred tax liabilities	(2,077)	(2,731)
Net deferred tax asset	$ 63,178	$ 64,132