Shareholders' Equity - Summary of common shareholders' equity (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ 33,532	$ 31,513
Purchase of treasury shares	(100)	(128)
Stock based compensation	85	58
Net income	1,898	98
Balance	$ 35,415	31,541
Balance (shares)	2,614,506
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ 523	523
Purchase of treasury shares	0	0
Stock based compensation	0	0
Net income	0	0
Balance	523	523
Capital in excess of par value
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	14,358	14,250
Purchase of treasury shares	0	0
Stock based compensation	33	14
Net income	0	0
Balance	14,391	14,264
Retained earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	20,484	18,788
Purchase of treasury shares	0	0
Stock based compensation	0	0
Net income	1,898	98
Balance	22,382	18,886
ESOT
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	(460)	(561)
Purchase of treasury shares	0	0
Stock based compensation	0	0
Net income	0	0
Balance	(460)	(561)
Treasury stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	(1,471)	(1,522)
Purchase of treasury shares	(100)	(128)
Stock based compensation	52	44
Net income	0	0
Balance	(1,519)	(1,606)
Accumulated Other Comprehensive Income (Loss)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	98	35
Purchase of treasury shares	0	0
Stock based compensation	0	0
Net income	0	0
Balance	$ 98	$ 35