Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Deferred Tax Assets, Gross [Abstract]
Allowance for credit losses	$ 17,784	$ 18,218
Postretirement benefits other than pensions	641	679
Alternative minimum tax credit carryforward	5,065	8,627
Litigation reserve	0	3,000
Unrealized loss on securities available for sale	1,291	2,463
Writedown of other real estate owned	1,087	603
Deferred compensation	2,113	2,246
Accrued interest on nonaccrual loans	1,452	1,059
Other-than-temporary impairment of securities	89	9,239
Depreciation of assets	879	1,127
Accrued incentives	1,629	1,594
Unfunded loan commitment allowance	1,557	1,078
Accrued severance	808	160
Basis difference in assets acquired	417	0
Loan origination fees and costs	141	0
Deferred rent	1,258	969
Other	1,105	1,194
Total deferred tax assets	37,316	52,256
Deferred tax liabilities:
Basis difference in assets acquired	0	(344)
Loan origination fees and costs	0	(1,337)
Income from unconsolidated subsidiary	(619)	(603)
Other	(337)	(318)
Total deferred tax liabilities	(956)	(2,602)
Net deferred tax asset	$ 36,360	$ 49,654