Note 1 - Nature of Business and Significant Accounting Policies - Option Pricing Model Valuation Assumptions (Details) - $ / shares	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Expected life of option grants (Year)	10 years
Weighted-average grant date fair value (in dollars per share)	$ 13.97	$ 10.85	$ 10.07
Employee Stock Option
Dividend yield		0.55%
Expected volatility		23.57%
Risk-free interest rate		1.62%
Expected life of option grants (Year)	6 years 3 months	6 years 3 months	6 years 3 months
Weighted-average grant date fair value (in dollars per share)		$ 10.85	$ 10.07
Employee Stock Option | Minimum
Dividend yield			0.60%
Expected volatility	22.65%		25.49%
Risk-free interest rate	1.87%		0.79%
Employee Stock Option | Maximum
Dividend yield	0.45%		0.81%
Expected volatility	23.52%		25.70%
Risk-free interest rate	3.12%		1.31%
Stock Purchase Grants [Member]
Weighted-average grant date fair value (in dollars per share)	$ 7.88	$ 7.67	$ 6.03
Stock Purchase Grants [Member] | Minimum
Dividend yield	0.43%	0.49%	0.55%
Expected volatility	17.97%	37.51%	24.59%
Risk-free interest rate	0.14%	0.00%	0.15%
Expected life of option grants (Year)	3 months	3 months	3 months
Weighted-average grant date fair value (in dollars per share)	$ 13.94
Stock Purchase Grants [Member] | Maximum
Dividend yield	0.44%	0.61%	0.81%
Expected volatility	21.16%	38.65%	36.38%
Risk-free interest rate	2.24%	0.06%	1.65%
Expected life of option grants (Year)	6 months	6 months	6 months
Weighted-average grant date fair value (in dollars per share)	$ 15.09