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						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Net income	$ 766,000	$ 1,671,000	$ 3,719,000	$ 8,107,000	$ 6,220,000	$ 5,342,000	$ 6,156,000	$ 19,668,000
Shares (denominator):
Basic weighted average common shares outstanding (in shares)	13,177,520			13,588,554			13,255,125	13,431,210
Add: dilutive effect of common stock options (in shares)	241,965			444,473			300,800	546,354
Diluted weighted average common shares outstanding (in shares)	13,419,485			14,033,027			13,555,925	13,977,564
Earnings per common share:
Basic (in dollars per share)	$ 0.06			$ 0.60			$ 0.46	$ 1.46
Diluted (in dollars per share)	$ 0.06			$ 0.58			$ 0.45	$ 1.41