Income Taxes - Significant Components of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Nov. 18, 2014
Deferred tax assets:
Loan loss reserves	$ 4,452	$ 6,680
Depreciation	413	748
Other real estate owned valuation	85	354
Tax credits carryforward	2,193	1,471
Unrealized loss on securities available for sale	241	1,685
Unrealized loss on securities held to maturity	217	431
Interest on nonaccrual loans	482	1,039
Net operating loss carryforward	914	8,574
Purchase accounting adjustment	442
Accrued bonuses	551	812
Other	176	221
Deferred tax assets	10,166	22,015
Deferred tax liabilities:
Deferred loan fees	1,145	1,275
Federal Home Loan Bank stock dividends	2,787	4,585
Mortgage servicing rights	1,401	2,124
FHLB prepayment penalty	307	786	$ 3,900
Purchase accounting adjustment		371
Prepaid expenses	306	139
Deferred tax liabilities	5,946	9,280
Net deferred tax asset	$ 4,220	$ 12,735