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Note 14 - Stock-based Compensation - Summary of Stock Option Weighted Average Assumptions of Employee Stock Options (Details) - $ / shares
3 Months Ended 9 Months Ended
May 31, 2019
Nov. 30, 2018
May 31, 2018
May 31, 2019
May 31, 2018
Term structure of risk-free interest rate [1]        
Term structure of volatility [1]        
Weighted average estimated fair value (in dollars per share) [1]        
Granted, weighted average price per share (in dollars per share) $ 267,020 $ 221,930 [1]    
Minimum [Member]          
Term structure of risk-free interest rate 2.48%     1.28% 1.28%
Term structure of volatility 18.00%     18.00% 19.00%
Maximum [Member]          
Term structure of risk-free interest rate 3.14%     3.14% 2.41%
Expected life (years) (Year) 7 years 36 days     7 years 36 days 7 years 146 days
Term structure of volatility 25.00%     29.00% 29.00%
Dividend yield 1.15%     1.15% 1.32%
Weighted average estimated fair value (in dollars per share) $ 68.33     $ 56.78 $ 48.29
Granted, weighted average price per share (in dollars per share) $ 267.02     $ 221.97 $ 190.04
Fair value as a percentage of exercise price 25.60%     25.60% 25.40%
[1] There were no employee stock options granted during the three months ended May 31, 2018.