Note 5 - Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Net income	$ 1,440,092	$ 1,027,732	$ 2,713,711	$ 2,258,997
Numerator for basic and diluted earnings per share	$ 1,440,092	$ 1,027,732	$ 2,713,711	$ 2,258,997
Denominator for basic EPS: weighted-average shares (in shares)	9,180,076	9,225,960	9,222,028	9,212,846
Effect of dilutive securities (in shares)	651	3,169	505	12,628
Denominator for diluted EPS-weighted-average shares (in shares)	9,180,727	9,229,129	9,222,533	9,225,474
Basic earnings per share (in dollars per share)	$ 0.15	$ 0.11	$ 0.29	$ 0.24
Diluted earnings per share (in dollars per share)	$ 0.15	$ 0.11	$ 0.29	$ 0.24
Employee Stock Option [Member]
Effect of dilutive securities (in shares)				9,810
Restricted Stock [Member]
Effect of dilutive securities (in shares)	651	3,169	505	2,818