Note 16 - Stock-based Compensation - Summary of Stock Option Weighted Average Assumptions of Employee Stock Options (Details) - $ / shares	12 Months Ended
Aug. 31, 2018	Aug. 31, 2017	Aug. 31, 2016
Dividend yield	1.32%	1.18%	1.09%
Weighted average estimated fair value (in dollars per share)	$ 48.39	$ 40.68	$ 46.08
Granted (in dollars per share)	$ 190.42	$ 156.77	$ 168.55
Fair value as a percentage of exercise price	25.40%	25.90%	27.30%
Minimum [Member]
Term structure of risk-free interest rate	1.28%	0.07%	0.07%
Expected life (years) (Year)	7 years 146 days	7 years 146 days	7 years 109 days
Term structure of volatility	19.00%	21.00%	21.00%
Maximum [Member]
Term structure of risk-free interest rate	2.41%	2.09%	2.10%
Expected life (years) (Year)	7 years 146 days	8 years 36 days	8 years 36 days
Term structure of volatility	29.00%	30.00%	30.00%

Discount rate from fair value on purchase date that participants pay for shares.

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-Topic 718
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The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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The risk-free interest rate assumption that is used in valuing an option on its own shares.

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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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