Shareholders' Equity - Summary of common shareholders' equity (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ 34,243	$ 33,737	$ 35,415	$ 33,532	$ 33,737	$ 33,532
Retirement obligation, net of taxes	16	15
Purchase of treasury shares		(81)		(100)
Stock based compensation	25	31	87	85
Net income	1,186	541	965	1,898	1,727	2,863
Balance	35,470	34,243	36,467	35,415	35,470	36,467
Retained earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	22,344	21,803	22,382	20,484	21,803	20,484
Retirement obligation, net of taxes	0	0
Purchase of treasury shares		0		0
Stock based compensation	0	0	0	0
Net income	1,186	541	965	1,898
Balance	23,530	22,344	23,347	22,382	23,530	23,347
Accumulated Other Comprehensive Income
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	(1,341)	(1,356)	98	98	(1,356)	98
Retirement obligation, net of taxes	16	15
Purchase of treasury shares		0		0
Stock based compensation	0	0	0	0
Net income	0	0	0	0
Balance	(1,325)	(1,341)	98	98	(1,325)	98
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	523	523	523	523	523	523
Retirement obligation, net of taxes	0	0
Purchase of treasury shares		0		0
Stock based compensation	0	0	0	0
Net income	0	0	0	0
Balance	523	523	523	523	523	523
Capital in excess of par value
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	14,492	14,481	14,391	14,358	14,481	14,358
Retirement obligation, net of taxes	0	0
Purchase of treasury shares		0		0
Stock based compensation	5	11	39	33
Net income	0	0	0	0
Balance	14,497	14,492	14,430	14,391	14,497	14,430
ESOT
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	(359)	(359)	(460)	(460)	(359)	(460)
Retirement obligation, net of taxes	0	0
Purchase of treasury shares		0		0
Stock based compensation	0	0	0	0
Net income	0	0	0	0
Balance	(359)	(359)	(460)	(460)	(359)	(460)
Treasury stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	(1,416)	(1,355)	(1,519)	(1,471)	(1,355)	(1,471)
Retirement obligation, net of taxes	0	0
Purchase of treasury shares		(81)		(100)
Stock based compensation	20	20	48	52
Net income	0	0	0	0
Balance	$ (1,396)	$ (1,416)	$ (1,471)	$ (1,519)	$ (1,396)	$ (1,471)