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Income Taxes - Income Tax Expense Differs from the Amount of Income Tax Determined by Applying the U.S. Federal Income Tax Rate to Pretax Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Computed tax expense at statutory federal rate	$ 3,459	$ 2,808
Increase in income taxes resulting from re-measurement of net deferred tax assets	752	0
Decrease in income taxes resulting from:
Tax-exempt interest and dividend income	(241)	(254)
Income from bank owned life insurance	(244)	(179)
Other	0	(22)
Income tax expense	$ 3,726	$ 2,353

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Effective Income Tax Rate Reconciliation, Bank Owned Life Insurance Income, Amount

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations, attributable to increase (decrease) in the income tax rates.

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Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to income (loss) exempt from income taxes.

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