Note 16 - Stock-based Compensation - Summary of Stock Option Weighted Average Assumptions of Non-employee Director Stock Options (Details)	12 Months Ended
Aug. 31, 2018	Aug. 31, 2017	Aug. 31, 2016
Dividend yield	1.32%	1.18%	1.09%
Non Employee Directors Stock Option Plan [Member] \| Employee Stock Option [Member]
Risk-free interest rate	2.34%	1.95%	1.62%
Expected life (Year)	5 years 146 days	5 years 146 days	5 years 146 days
Expected volatility	19.70%	22.70%	23.00%
Dividend yield	1.16%	1.24%	1.05%

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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- Definition

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

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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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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
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-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809

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