Note 16 - Stock-based Compensation (Tables)

12 Months Ended

Aug. 31, 2018

Notes Tables

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

	2018				2017				2016
Term structure of risk-free interest rate		1.28%	–	2.41%		0.07%	–	2.09%		0.07%	–	2.1%
Expected life (years)		7.4	–	7.4		7.4	–	8.1		7.3	–	8.1
Term structure of volatility		19%	–	29%		21%	–	30%		21%	–	30%
Dividend yield			1.32%				1.18%				1.09%
Weighted average estimated fair value			$48.39				$40.68				$46.08
Weighted average exercise price			$190.42				$156.77				$168.55
Fair value as a percentage of exercise price			25.4%				25.9%				27.3%

The 2008 Employee Stock Purchase Plan [Member]

Notes Tables

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

	2018			2017			2016
Risk-free interest rate		1.55	%		0.69	%		0.22	%
Expected life (months)		3			3			3
Expected volatility		10.19	%		8.6	%		10.7	%
Dividend yield		1.27	%		1.25	%		1.18	%

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	2.34	%
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	%

Risk-free interest rate	1.62	%
Expected life (years)	5.4
Expected volatility	23.0	%
Dividend yield	1.05	%