Note 5 - Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Net income	$ 521,414	$ 1,000,350	$ 2,780,411	$ 4,342,262
Numerator for basic and diluted earnings per share	$ 521,414	$ 1,000,350	$ 2,780,411	$ 4,342,262
Denominator for basic EPS: weighted-average shares (in shares)	9,270,862	9,188,483	9,232,397	9,341,364
Effect of dilutive securities:
Effect of dilutive securities (in shares)	3,088	17,899	13,669	18,041
Denominator for diluted EPS-weighted-average shares (in shares)	9,273,950	9,206,382	9,246,066	9,359,405
Basic earnings per share (in dollars per share)	$ 0.06	$ 0.11	$ 0.30	$ 0.46
Diluted earnings per share (in dollars per share)	$ 0.06	$ 0.11	$ 0.30	$ 0.46
Employee Stock Option [Member]
Effect of dilutive securities:
Effect of dilutive securities (in shares)		16,933	9,810	17,279
Restricted Stock [Member]
Effect of dilutive securities:
Effect of dilutive securities (in shares)	3,088	966	3,859	762