Shareholders' Equity - Summary of common shareholders' equity (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ 35,415	$ 33,532	$ 31,541	$ 31,513	$ 33,532	$ 31,513
Dividends declared ($0.16 per share)			(413)
Purchase of treasury shares		(100)	(21)	(128)
Stock based compensation	87	85	95	58
Net income	965	1,898	714	98	2,863	812
Balance	36,467	35,415	31,916	31,541	36,467	31,916
Retained earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	22,382	20,484	18,886	18,788	20,484	18,788
Dividends declared ($0.16 per share)			(413)
Purchase of treasury shares		0	0	0
Stock based compensation	0	0	0	0
Net income	965	1,898	714	98
Balance	23,347	22,382	19,187	18,886	23,347	19,187
Accumulated Other Comprehensive Income (Loss)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	98	98	35	35	98	35
Dividends declared ($0.16 per share)			0
Purchase of treasury shares		0	0	0
Stock based compensation	0	0	0	0
Net income	0	0	0	0
Balance	98	98	35	35	98	35
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	523	523	523	523	523	523
Dividends declared ($0.16 per share)			0
Purchase of treasury shares		0	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	14,391	14,358	14,264	14,250	14,358	14,250
Dividends declared ($0.16 per share)			0
Purchase of treasury shares		0	0	0
Stock based compensation	39	33	34	14
Net income	0	0	0	0
Balance	14,430	14,391	14,298	14,264	14,430	14,298
ESOT
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	(460)	(460)	(561)	(561)	(460)	(561)
Dividends declared ($0.16 per share)			0
Purchase of treasury shares		0	0	0
Stock based compensation	0	0	0	0
Net income	0	0	0	0
Balance	(460)	(460)	(561)	(561)	(460)	(561)
Treasury stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	(1,519)	(1,471)	(1,606)	(1,522)	(1,471)	(1,522)
Dividends declared ($0.16 per share)			0
Purchase of treasury shares		(100)	(21)	(128)
Stock based compensation	48	52	61	44
Net income	0	0	0	0
Balance	$ (1,471)	$ (1,519)	$ (1,566)	$ (1,606)	$ (1,471)	$ (1,566)