Note 14 - Stock-based Compensation (Tables)

6 Months Ended

Feb. 28, 2018

Notes Tables

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

Three months ended February 28,	2018				2017
Term structure of risk-free interest rate		1.28%	-	2.41%		0.49%	-	1.89%
Expected life (years)				7.4				7.4
Term structure of volatility		19%	-	29%		21%	-	29%
Dividend yield				1.32%				1.18%
Weighted average estimated fair value				$48.82				$43.81
Weighted average exercise price				$192.11				$169.16
Fair value as a percentage of exercise price				25.4%				25.9%

Six months ended February 28,	2018				2017
Term structure of risk-free interest rate		1.28%	-	2.41%		0.07%	-	2.09%
Expected life (years)				7.4				7.4
Term structure of volatility		19%	-	29%		21%	-	30%
Dividend yield				1.32%				1.18%
Weighted average estimated fair value				$48.29				$39.95
Weighted average exercise price				$190.04				$153.87
Fair value as a percentage of exercise price				25.4%				26.0%

The 2008 Employee Stock Purchase Plan [Member]

Notes Tables

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

Three months ended February 28,	2018			2017
Risk-free interest rate		1.45	%		0.51	%
Expected life (months)		3			3
Expected volatility		13.9	%		7.8	%
Dividend yield		1.11	%		1.25	%
Weighted average estimated fair value	$	35.02		$	25.88

Six months ended February 28,	2018			2017
Risk-free interest rate		1.26	%		0.44	%
Expected life (months)		3			3
Expected volatility		10.52	%		8.9	%
Dividend yield		1.29	%		1.19	%
Weighted average estimated fair value	$	29.76		$	27.85

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	%