Fair Values of Financial Instruments - Notional Amount of Off-Balance Sheet Commitment Financial Instruments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Values Of Financial Instruments [Line Items]
Fixed Rate	$ 17,063	$ 17,147
Variable Rate	72,667	75,379
Commitments to make loans
Fair Values Of Financial Instruments [Line Items]
Fixed Rate	8,611	11,940
Variable Rate	1,022	12,785
Unused lines of credit
Fair Values Of Financial Instruments [Line Items]
Fixed Rate	8,452	5,207
Variable Rate	$ 71,645	$ 62,594