Shareholders' Equity - Summary of common shareholders' equity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ 27,117	$ 25,442
Balance (shares)	2,614,506
Net income	$ 1,317	1,753
Retirement benefits adjustment	(12)	(17)
Compensation expense	101	100
Purchase of treasury shares	(195)	(275)
Cash dividend	(376)	(380)
Stock based compensation, net of tax benefit	213	494
Balance	$ 28,165	$ 27,117
Balance (shares)	2,614,506	2,614,506
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ 523	$ 523
Balance (shares)	2,614,506	2,614,506
Balance		$ 523
Balance (shares)		2,614,506
Capital in excess of par value
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ 14,160	$ 14,092
Stock based compensation, net of tax benefit	11	68
Balance	14,171	14,160
Retained earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	14,768	13,395
Net income	1,317	1,753
Cash dividend	(376)	(380)
Balance	15,709	14,768
ESOT
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	(763)	(863)
Compensation expense	101	100
Balance	(662)	(763)
Treasury stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	(1,551)	(1,702)
Purchase of treasury shares	(195)	(275)
Stock based compensation, net of tax benefit	202	426
Balance	(1,544)	(1,551)
Accumulated Other Comprehensive Loss
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	(20)	(3)
Retirement benefits adjustment	(12)	(17)
Balance	$ (32)	$ (20)