Income Taxes - Components of net deferred income tax benefits (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred income tax benefits:
Accrued deferred compensation	$ 92	$ 146
Allowance for credit losses	7	95
Nonaccrual interest	375	445
Alternative minimum tax credits	1,191	967
Net operating loss carryforward credits	297	665
Accumulated depreciation	(15)
Accumulated depreciation		54
Other real estate owned	3	18
Reserve for unfunded commitments	7	10
Other temporary differences	20	22
Accumulated securities premium accretion	213	211
Net unrealized depreciation on investment securities available for sale	239	527
Deferred income tax liabilities:
Deferred Tax Assets, Net, Total	$ 2,429	$ 3,160