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Note 4 - Stock-based Compensation- Stock Option Assumption (Details) - Share-based Payment Arrangement, Option [Member] - $ / shares
3 Months Ended
Mar. 31, 2022
Mar. 31, 2021
Risk-free interest rate 1.60% 0.40%
Dividend yield 1.90% 1.90%
Expected life (years) (Year) 4 years 4 months 24 days 4 years 7 months 6 days
Volatility 28.70% 28.30%
Weighted-average grant-date fair value of options granted (in dollars per share) $ 51.92 $ 39.97