Income Taxes - Reconciliation of Federal Income Tax Rate (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Expected federal income tax expense at statutory tax rate									$ 1,415	$ 1,853	$ 1,110
Effect of nontaxable interest income									(220)	(345)	(452)
Effect of nontaxable bank owned life insurance income									(64)	(164)	(117)
Effect of Qualified Zone Academy Bond (QZAB)											(114)
State taxes on income, net of federal benefit									75	59	59
Other tax credits									(129)	(243)	(128)
Deferred tax asset revaluation										980
Other									(23)
Non-deductible expenses									13	8	4
Income tax expense (benefit)	$ 368	$ 180	$ 323	$ 196	$ 1,159	$ 486	$ 368	$ 135	$ 1,067	$ 2,148	$ 362
Income tax rate									15.80%	39.40%	11.10%