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				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
Net income	$ 1,671,000	$ 3,719,000	$ 6,220,000	$ 5,342,000	$ 5,390,000	$ 11,561,000
Shares (denominator):
Basic weighted average common shares outstanding (in shares)	13,246,676		13,351,675		13,294,571	13,351,674
Add: dilutive effect of common stock options (in shares)	264,821		300,320		326,530	461,420
Diluted weighted average common shares outstanding (in shares)	13,511,497		13,651,995		13,621,101	13,813,094
Earnings per common share:
Basic (in dollars per share)	$ 0.13		$ 0.47		$ 0.41	$ 0.87
Diluted (in dollars per share)	$ 0.12		$ 0.46		$ 0.40	$ 0.84