Note 9 - Share-based Compensation - Stock Options Valuation Assumptions (Details) - Common Stock [Member]	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Expected dividend yield at date of grant	3.39%	2.15%	1.84%
Expected stock price volatility	35.52%	34.85%	33.62%
Risk-free interest rate	2.33%	0.91%	1.35%
Expected life of options (in years) (Year)	6 years 3 months 18 days	7 years 3 days	7 years 4 months 20 days