Stockholders' Equity - Summary of common shareholders' equity (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ 31,916	$ 31,541	$ 31,513	$ 28,722	$ 28,379	$ 28,165	$ 31,513	$ 28,165
Balance (shares)			2,614,506				2,614,506
Net income	1,132	714	$ 98	1,457	707	331	$ 1,944	2,495
Purchase of treasury shares	(8)	(21)	(128)	0	(33)	(117)
Dividends declared ($0.16 per share)	0	(413)		(3)	(416)
Stock based compensation	86	95	58	98	85
Balance	$ 33,126	31,916	31,541	30,280	28,722	28,379	$ 33,126	30,280
Balance (shares)	2,614,506						2,614,506
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ 523	523	523	523	523	523	$ 523	523
Net income	0	0	0	0	0	0
Purchase of treasury shares	0	0	0	0	0	0
Dividends declared ($0.16 per share)	0	0		0	0
Stock based compensation	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	14,298	14,264	14,250	14,192	14,171	14,171	14,250	14,171
Net income	0	0	0	0	0	0
Purchase of treasury shares	0	0	0	0	0	0
Dividends declared ($0.16 per share)	0	0		0	0
Stock based compensation	28	34	14	34	21
Balance	14,326	14,298	14,264	14,226	14,192	14,171	14,326	14,226
Retained earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	19,187	18,886	18,788	16,325	16,040	15,709	18,788	15,709
Net income	1,132	714	98	1,457	707	331
Purchase of treasury shares	0	0	0	0	0	0
Dividends declared ($0.16 per share)	0	(413)		(3)	(416)
Stock based compensation	0	0	0	0	(6)
Balance	20,319	19,187	18,886	17,785	16,325	16,040	20,319	17,785
ESOT
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	(561)	(561)	(561)	(662)	(662)	(662)	(561)	(662)
Net income	0	0	0	0	0	0
Purchase of treasury shares	0	0	0	0	0	0
Dividends declared ($0.16 per share)	0	0		0	0
Stock based compensation	0	0	0	0	0
Balance	(561)	(561)	(561)	(662)	(662)	(662)	(561)	(662)
Treasury stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	(1,566)	(1,606)	(1,522)	(1,630)	(1,661)	(1,544)	(1,522)	(1,544)
Net income	0	0	0	0	0	0
Purchase of treasury shares	(8)	(21)	(128)	0	(33)	(117)
Dividends declared ($0.16 per share)	0	0		0	0
Stock based compensation	58	61	44	64	64
Balance	(1,516)	(1,566)	(1,606)	(1,566)	(1,630)	(1,661)	(1,516)	(1,566)
Accumulated Other Comprehensive Income (Loss)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	35	35	35	(26)	(32)	(32)	35	(32)
Net income	0	0	0	0	0	0
Purchase of treasury shares	0	0	0	0	0	0
Dividends declared ($0.16 per share)	0	0		0	0
Stock based compensation	0	0	0	0	6
Balance	$ 35	$ 35	$ 35	$ (26)	$ (26)	$ (32)	$ 35	$ (26)