Stock-based Compensation (Narrative) (Details) - USD ($)	12 Months Ended
Aug. 31, 2019	Aug. 31, 2018	Aug. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized under stock plan	1,000,000
Number of shares available for grant	720,373
Allocated share-based compensation expense	$ 4,400,000	$ 4,200,000	$ 4,100,000
Employee service share-based, Tax benefit from compensation expense	$ 1,000,000.0	1,100,000	1,400,000
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee service share-based, Tax benefit from compensation expense		100,000	400,000
Total intrinsic value of stock options exercised		500,000	1,600,000
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Employee service share-based, Tax benefit from compensation expense	$ 1,400,000	$ 700,000	$ 1,300,000
Compensation cost not yet recognized	$ 600,000
Remaining weighted-average vesting periods	1 year 7 months 6 days
Weighted-average grant date fair value	$ 163.93	$ 111.71	$ 109.23
Total intrinsic value of stock-based awards converted into common shares	$ 6,000,000.0	$ 2,800,000	$ 3,600,000
Market Share Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Employee service share-based, Tax benefit from compensation expense	$ 900,000	$ 800,000	$ 900,000
Compensation cost not yet recognized	$ 2,100,000
Remaining weighted-average vesting periods	1 year 10 months 24 days
Weighted-average grant date fair value	$ 177.82	$ 101.93	$ 90.91
Total intrinsic value of stock-based awards converted into common shares	$ 4,000,000.0	$ 3,000,000.0	$ 2,800,000
Expected volatility period	2 years 10 months 24 days	2 years 10 months 20 days	2 years 10 months 20 days
Deferred Performance Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	1 year
Compensation cost not yet recognized	$ 0
Weighted-average grant date fair value	$ 160.37	$ 110.65	$ 110.19
Minimum [Member] \| Market Share Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percent of original target number of vested shares	0.00%
Minimum [Member] \| Deferred Performance Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percent of original target number of vested shares	0.00%
Maximum [Member] \| Market Share Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percent of original target number of vested shares	200.00%
Maximum [Member] \| Deferred Performance Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percent of original target number of vested shares	100.00%

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Amount of tax benefit for recognition of expense of award under share-based payment arrangement.

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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Number of shares authorized for issuance under share-based payment arrangement.

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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Percentage of vesting of share-based compensation awards.

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