computation of earnings per share (basic and diluted) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Earnings Per Share [Abstract]
Net income	$ 4,526	$ 2,047
Less: Undistributed earnings allocated to participating securities	(64)	(34)
Net income allocated to common stock	4,462	2,013
Weighted-average common shares issued	2,845	2,828
Less: Unvested restricted stock awards	(40)	(40)
Weighted average common shares outstanding used to calculate basic earnings per common share	2,805	2,788
Add: Dilutive effect of stock options and restricted stock units	10	9
Weighted-average common shares outstanding used to calculate diluted earnings per common share	$ 2,815	$ 2,797
Earnings per common share (basic)	$ 1.59	$ 0.72
Earnings per common share (diluted)	$ 1.59	$ 0.72