Note 2 - Computation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 31, 2019		Sep. 30, 2019		Jun. 30, 2019		Mar. 31, 2019		Dec. 31, 2018		Sep. 30, 2018		Jun. 30, 2018		Mar. 31, 2018		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Earnings Per Share [Abstract]
Numerator for basic and diluted earnings per share - net income	$ 2,745		$ 3,090		$ 3,143		$ 3,379		$ 2,327		$ 3,211		$ 2,862		$ 2,935		$ 12,357	$ 11,335	$ 8,289
Denominator for basic earnings per share - weighted average shares outstanding																	3,498,326	3,463,450	3,428,970
Effect of dilutive securities - employee stock options																	5,824	19,059	16,841
Denominator for diluted earnings per share - adjusted weighted average shares outstanding																	3,504,150	3,482,509	3,445,811
Earnings per share - basic	$ 0.78	[1]	$ 0.88	[1]	$ 0.90	[1]	$ 0.97	[1]	$ 0.67	[1]	$ 0.93	[1]	$ 0.83	[1]	$ 0.85	[1]	$ 3.53	$ 3.27	$ 2.42
Earnings per share - diluted	$ 0.78	[1]	$ 0.88	[1]	$ 0.90	[1]	$ 0.97	[1]	$ 0.67	[1]	$ 0.92	[1]	$ 0.82	[1]	$ 0.85	[1]	$ 3.53	$ 3.25	$ 2.41

[1] Due to rounding, quarterly earnings per share may not sum to annual earnings per share