Note 5 - Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Net income	$ 1,273,619	$ 1,231,265
Numerator for basic and diluted earnings per share	$ 1,273,619	$ 1,231,265
Denominator for basic earnings per share – weighted-average shares (in shares)	9,264,446	9,308,726
Effect of dilutive securities (in shares)	365	22,193
Denominator for diluted earnings per share – weighted-average shares (in shares)	9,264,811	9,330,919
Basic earnings per share (in dollars per share)	$ 0.14	$ 0.13
Diluted earnings per share (in dollars per share)	$ 0.14	$ 0.13
Employee Stock Option [Member]
Effect of dilutive securities (in shares)		19,729
Restricted Stock [Member]
Effect of dilutive securities (in shares)	365	2,464