Shareholders' Equity - Summary of common shareholders' equity (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ 35,470	$ 34,243	$ 33,737	$ 36,467	$ 35,415	$ 33,532	$ 33,737	$ 33,532
Retirement obligation, net of taxes	15	16	15
Purchase of treasury shares			(81)			(100)
Stock based compensation	25	25	31	83	87	85
Net Income	3,238	1,186	541	(1,782)	965	1,898	4,965	1,081
Balance	38,748	35,470	34,243	34,768	36,467	35,415	38,748	34,768
Retained earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	23,530	22,344	21,803	23,347	22,382	20,484	21,803	20,484
Retirement obligation, net of taxes	0	0	0
Purchase of treasury shares			0			0
Stock based compensation	0	0	0	0	0	0
Net Income	3,238	1,186	541	(1,782)	965	1,898
Balance	26,768	23,530	22,344	21,565	23,347	22,382	26,768	21,565
Accumulated Other Comprehensive Income (Loss)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	(1,325)	(1,341)	(1,356)	98	98	98	(1,356)	98
Retirement obligation, net of taxes	15	16	15
Purchase of treasury shares			0			0
Stock based compensation	0	0	0	0	0	0
Net Income	0	0	0	0	0	0
Balance	(1,310)	(1,325)	(1,341)	98	98	98	(1,310)	98
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	523	523	523	523	523	523	523	523
Retirement obligation, net of taxes	0	0	0
Purchase of treasury shares			0			0
Stock based compensation	0	0	0	0	0	0
Net Income	0	0	0	0	0	0
Balance	523	523	523	523	523	523	523	523
Capital in excess of par value
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	14,497	14,492	14,481	14,430	14,391	14,358	14,481	14,358
Retirement obligation, net of taxes	0	0	0
Purchase of treasury shares			0			0
Stock based compensation	1	5	11	29	39	33
Net Income	0	0	0	0	0	0
Balance	14,498	14,497	14,492	14,459	14,430	14,391	14,498	14,459
ESOT
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	(359)	(359)	(359)	(460)	(460)	(460)	(359)	(460)
Retirement obligation, net of taxes	0	0	0
Purchase of treasury shares			0			0
Stock based compensation	0	0	0	0	0	0
Net Income	0	0	0	0	0	0
Balance	(359)	(359)	(359)	(460)	(460)	(460)	(359)	(460)
Treasury stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	(1,396)	(1,416)	(1,355)	(1,471)	(1,519)	(1,471)	(1,355)	(1,471)
Retirement obligation, net of taxes	0	0	0
Purchase of treasury shares			(81)			(100)
Stock based compensation	24	20	20	54	48	52
Net Income	0	0	0	0	0	0
Balance	$ (1,372)	$ (1,396)	$ (1,416)	$ (1,417)	$ (1,471)	$ (1,519)	$ (1,372)	$ (1,417)