Note 5 - Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Net income	$ 1,027,732	$ 1,820,915	$ 2,258,997	$ 3,341,912
Numerator for basic and diluted earnings per share	$ 1,027,732	$ 1,820,915	$ 2,258,997	$ 3,341,912
Denominator for basic EPS: weighted-average shares (in shares)	9,225,960	9,209,446	9,212,846	9,418,645
Effect of dilutive securities:
Effect of dilutive securities (in shares)	3,169	18,495	12,628	18,975
Denominator for diluted EPS-weighted-average shares (in shares)	9,229,129	9,227,941	9,225,474	9,437,620
Basic earnings per share (in dollars per share)	$ 0.11	$ 0.19	$ 0.24	$ 0.35
Diluted earnings per share (in dollars per share)	$ 0.11	$ 0.19	$ 0.24	$ 0.35
Employee Stock Option [Member]
Effect of dilutive securities:
Effect of dilutive securities (in shares)		18,495	9,810	18,975
Restricted Stock [Member]
Effect of dilutive securities:
Effect of dilutive securities (in shares)	3,169		2,818