Shareholders' Equity - Summary of common shareholders' equity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ 33,532	$ 31,513
Dividends declared ($0.16 per share)		(413)
Retirement benefits adjustment	(134)	(174)
Purchase of treasury shares	(100)	(157)
Stock based compensation	339	316
Net income	100	2,447
Balance	33,737	33,532
Retained earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	21,703	19,669
Dividends declared ($0.16 per share)		(413)
Net income	100	2,447
Balance	21,803	21,703
Accumulated Other Comprehensive Income
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	(1,121)	(846)
Retirement benefits adjustment	(235)	(275)
Balance	(1,356)	(1,121)
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	523	523
Balance	523	523
Capital in excess of par value
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	14,358	14,250
Stock based compensation	123	108
Balance	14,481	14,358
ESOT
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	(460)	(561)
Retirement benefits adjustment	101	101
Balance	(359)	(460)
Treasury stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	(1,471)	(1,522)
Purchase of treasury shares	(100)	(157)
Stock based compensation	216	208
Balance	$ (1,355)	$ (1,471)