Note 16 - Stock-based Compensation (Tables)

12 Months Ended

Aug. 31, 2019

Notes Tables

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]

	2019				2018				2017
Term structure of risk-free interest rate		1.28%	—	3.14%		1.28%	—	2.41%		0.07%	—	2.09%
Expected life (years)		7.1	—	7.1		7.4	—	7.4		7.4	—	8.1
Term structure of volatility		18%	—	29%		19%	—	29%		21%	—	30%
Dividend yield			1.15%				1.32%				1.18%
Weighted average estimated fair value			$57.12				$48.39				$40.68
Weighted average exercise price			$224.35				$190.42				$156.77
Fair value as a percentage of exercise price			25.5%				25.4%				25.9%

The 2008 Employee Stock Purchase Plan [Member]

Notes Tables

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]

	2019			2018			2017
Risk-free interest rate		2.33	%		1.55	%		0.69	%
Expected life (months)		3			3			3
Expected volatility		10.89	%		10.19	%		8.60	%
Dividend yield		1.12	%		1.27	%		1.25	%

Non Employee Directors Stock Option Plan [Member]

Notes Tables

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]

Risk-free interest rate	2.51	%
Expected life (years)	5.4
Expected volatility	20.5	%
Dividend yield	1.17	%

Risk-free interest rate	2.34	%
Expected life (years)	5.4
Expected volatility	19.7	%
Dividend yield	1.16	%

Risk-free interest rate	1.95	%
Expected life (years)	5.4
Expected volatility	22.7	%
Dividend yield	1.24	%