Note 14 - Stock-based Compensation - Summary of Stock Option Weighted Average Assumptions, Employee Stock Purchase Plan (Details) - $ / shares	3 Months Ended	6 Months Ended
Feb. 28, 2018	Feb. 28, 2017	Feb. 28, 2018	Feb. 28, 2017
Expected life (years) (Year)	7 years 146 days	7 years 146 days	7 years 146 days	7 years 146 days
Dividend yield	1.32%	1.18%	1.32%	1.18%
Weighted average estimated fair value (in dollars per share)	$ 48.82	$ 43.81	$ 48.29	$ 39.95
The 2008 Employee Stock Purchase Plan [Member]
Risk-free interest rate	1.45%	0.51%	1.26%	0.44%
Expected life (years) (Year)	90 days	90 days	90 days	90 days
Expected volatility	13.90%	7.80%	10.52%	8.90%
Dividend yield	1.11%	1.25%	1.29%	1.19%
Weighted average estimated fair value (in dollars per share)	$ 35.02	$ 25.88	$ 29.76	$ 27.85

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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- Definition

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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- Definition

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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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(i)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.D.2)
-URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809

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