Income Taxes - Significant Components of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Deferred tax assets:
Loan loss reserves	$ 4,480	$ 4,452
Depreciation	671	413
Other real estate owned valuation	62	85
Tax credits carryforward		2,193
Unrealized loss on securities available for sale	2,153	241
Unrealized loss on securities held to maturity	192	217
Interest on nonaccrual loans	465	482
Net operating loss carryforward		914
Purchase accounting adjustment	137	442
Accrued bonuses	830	551
Other	38	176
Deferred tax assets	9,028	10,166
Deferred tax liabilities:
Deferred loan fees	1,482	1,145
Federal Home Loan Bank stock dividends	2,749	2,787
Mortgage servicing rights	1,547	1,401
FHLB prepayment penalty	205	307
Prepaid expenses	372	306
Deferred tax liabilities	6,355	5,946
Net deferred tax asset	$ 2,673	$ 4,220