Income Taxes - Significant Components of Deferred Tax Assets and Liabilities (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Deferred tax assets:
Loan loss reserves	$ 6,346	$ 7,391
Postretirement benefits	1,090	1,162
Other real estate owned valuation	1,227	1,421
Tax credits carryforward	576	339
Securities impairment charges	0	153
Unrealized loss on securities available for sale	5,869	14,138
Interest on nonaccrual loans	897	758
Net operating loss carryforward	22,827	26,708
Purchase accounting adjustment	79	70
Accrued bonuses	278	456
Other	697	295
Less: Valuation allowance	(1,146)	(42,802)
Deferred tax assets	38,740	10,089
Deferred tax liabilities:
Deferred loan fees	321	405
Federal Home Loan Bank stock dividends	4,585	6,715
Mortgage servicing rights	1,984	2,079
Postretirement benefits accrual	640	640
Prepaid expenses	181	250
Deferred tax liabilities	7,711	10,089
Net deferred tax asset	$ 31,029	$ 0