Note 4 - Computation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share [Abstract]
Numerator for basic and diluted earnings per share - net income	$ 2,862	$ 2,386	$ 5,797	$ 5,246
Denominator for basic earnings per share - weighted average shares outstanding	3,460,360	3,425,356	3,456,467	3,420,239
Effect of dilutive securities - employee stock options	20,952	17,852	20,407	16,027
Denominator for diluted earnings per share - adjusted weighted average shares outstanding	3,481,312	3,443,208	3,476,874	3,436,266
Earnings per share - basic	$ 0.83	$ 0.70	$ 1.68	$ 1.53
Earnings per share - diluted	$ 0.82	$ 0.69	$ 1.67	$ 1.53