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, 2021	Mar. 31, 2020
Net income	$ 3,719,000	$ 5,342,000
Shares (denominator):
Basic weighted average common shares outstanding (in shares)	13,342,398	13,121,867
Add: dilutive effect of common stock options (in shares)	375,006	542,843
Diluted weighted average common shares outstanding (in shares)	13,717,404	13,664,710
Earnings per common share:
Basic (in dollars per share)	$ 0.28	$ 0.41
Diluted (in dollars per share)	$ 0.27	$ 0.39