Note 1 - Nature of Business and Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2020

Notes Tables

Fair value of stock option grants

	2020		2019		2018
Dividend yield		0.60% to 0.81%		0.67%		0.45% to 0.48%
Expected volatility		25.49% to 25.70%		28.28%		29.51% to 29.59%
Risk-free interest rate		0.79% to 1.31%		2.90%		2.60% to 2.94%
Expected life of option grants		6.25 years		6.25 years		6 years
Weighted-average grant date fair value	$	10.07	$	11.29	$	14.68

	2020		2019		2018
Dividend yield		0.55% to 0.81%		0.69% to 0.75%		0.37% to 0.51%
Expected volatility		24.59% to 36.38%		20.15% to 21.06%		20.90% to 21.40%
Risk-free interest rate		0.15% to 1.65%		2.02 % to 2.46%		1.59% to 2.22%
Expected life of purchase grants		3 to 6 months		3 to 6 months		3 to 6 months
Weighted-average grant date fair value	$	6.03	$	4.81	$	6.63