Note 15 - Stock-based Compensation - Summary of Stock Option Weighted Average Assumptions, Employee Stock Purchase Plan (Details) - $ / shares	3 Months Ended		9 Months Ended
	May 31, 2017	May 31, 2016	May 31, 2017	May 31, 2016
Expected volatility
Dividend yield	1.18%	1.33%	1.18%	1.09%
Weighted average estimated fair value (in dollars per share)	$ 42.23	$ 40.57	$ 39.98	$ 46.05
Expected life (Month)	7 years 146 days	7 years 182 days	7 years 146 days	7 years 255 days
The 2008 Employee Stock Purchase Plan [Member]
Expected volatility	8.30%	11.53%	8.70%	11.42%
Dividend yield	1.24%	1.29%	1.21%	1.15%
Weighted average estimated fair value (in dollars per share)	$ 29.84	$ 26.07	$ 28.48	$ 27.19
Risk-free interest rate	0.81%	0.27%	0.56%	0.20%
Expected life (Month)	90 days	90 days	90 days	90 days