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

12 Months Ended

Dec. 31, 2019

Notes Tables

Fair value of stock option grants

	2019		2018		2017
Dividend yield		0.67%		0.45% to 0.48%		0.36% to 0.47%
Expected volatility		28.28%		29.51% to 29.59%		29.64% to 29.95%
Risk-free interest rate		2.90%		2.60% to 2.94%		2.50% to 2.81%
Expected life of option grants		6.25 years		6 years		6 years
Weighted-average grant date fair value	$	11.29	$	14.68	$	14.75

	2019		2018		2017
Dividend yield		0.69% to 0.75%		0.37% to 0.51%		0.37% to 0.42%
Expected volatility		20.15% to 21.06%		20.90% to 21.40%		19.80% to 19.86%
Risk-free interest rate		2.02 % to 2.46%		1.59% to 2.22%		0.67% to 1.18%
Expected life of purchase grants		3 to 6 months		3 to 6 months		3 to 6 months
Weighted-average grant date fair value	$	4.81	$	6.63	$	6.42