Note 9 - Basic and Diluted Earnings Per Common Share - Reconciliation of Net Income and Number of Shares Used in Computations of Basic and Diluted EPS (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Net income	$ 508,000	$ 550,000
Shares (denominator):
Basic weighted average common shares outstanding (in shares)	14,217,919	15,207,659
Add: dilutive effect of common stock options (in shares)	165,086	94,142
Diluted weighted average common shares outstanding (in shares)	14,383,005	15,301,801
Earnings per common share:
Basic (in dollars per share)	$ 0.04	$ 0.04
Diluted (in dollars per share)	$ 0.04	$ 0.04