Note 14 - Stock-based Compensation - Summary of Stock Option Weighted Average Assumptions of Employee Stock Options (Details) - $ / shares	3 Months Ended	6 Months Ended
Feb. 28, 2019	Feb. 28, 2018	Feb. 28, 2019	Feb. 28, 2018
Expected life (years) (Year)
Dividend yield
Weighted average estimated fair value (in dollars per share)	$ 53.18	$ 48.82	$ 56.72	$ 48.29
Granted, weighted average price per share (in dollars per share)	$ 207.84	$ 192.11	$ 221.74	$ 190.04
Fair value as a percentage of exercise price
Minimum [Member]
Term structure of risk-free interest rate	2.48%	1.28%	1.28%	1.28%
Term structure of volatility	18.00%	19.00%	18.00%	19.00%
Weighted average estimated fair value (in dollars per share)	$ 53.18	$ 48.82	$ 56.72	$ 48.29
Granted, weighted average price per share (in dollars per share)	$ 207.84	$ 192.11	$ 221.74	$ 190.04
Maximum [Member]
Term structure of risk-free interest rate	3.14%	2.41%	3.14%	2.41%
Expected life (years) (Year)	7 years 36 days	7 years 146 days	7 years 36 days	7 years 146 days
Term structure of volatility	25.00%	29.00%	29.00%	29.00%
Dividend yield	1.15%	1.32%	1.16%	1.32%
Weighted average estimated fair value (in dollars per share)	$ 53.18	$ 48.82	$ 56.72	$ 48.29
Granted, weighted average price per share (in dollars per share)	$ 207.84	$ 192.11	$ 221.74	$ 190.04
Fair value as a percentage of exercise price	25.60%	25.40%	25.60%	25.40%

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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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- Definition

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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No definition available.

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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.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
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-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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