Note 8 - Shareholders' Equity - Weighted Average Assumptions Used in the Option Pricing to Value Stock Options Granted (Details) - $ / shares		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Expected volatility (1)	[1]	20.00%	20.00%	20.00%
Expected life in years (2) (Year)	[2]	4 years 8 months 12 days	3 years 6 months	4 years 8 months 12 days
Risk-free interest rate (3)	[3]	0.46%	1.52%	2.67%
Expected dividend yield		2.79%	2.59%	2.55%
Fair value per award (in dollars per share)		$ 7.50	$ 8.64	$ 10.19

[1] Measured using daily price changes of Company's stock over respective expected term of the option and the implied volatility derived from the market prices of the Company's stock and traded options.

[2] The number of years that the Company estimates that the options will be outstanding prior to exercise.

[3] The risk-free rate over the expected life based on the US Treasury yield curve in effect at the time of the grant.