Stock-based Compensation (Narrative) (Details) - USD ($)	12 Months Ended
Aug. 31, 2018	Aug. 31, 2017	Aug. 31, 2016
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	786,364
Allocated share-based compensation expense	$ 4,200,000	$ 4,100,000	$ 3,700,000
Employee service share-based, Tax benefit from compensation expense	1,100,000	1,400,000	1,200,000
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	700,000
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	$ 700,000	$ 1,300,000	$ 1,000,000
Compensation cost not yet recognized	$ 600,000
Remaining weighted-average vesting periods	1 year 7 months 6 days
Weighted-average grant date fair value	$ 111.71	$ 109.23	$ 95.89
Total intrinsic value of stock-based awards converted into common shares	$ 2,800,000	$ 3,600,000	$ 2,800,000
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	$ 800,000	$ 900,000	$ 1,200,000
Compensation cost not yet recognized	$ 1,700,000
Remaining weighted-average vesting periods	1 year 9 months 18 days
Weighted-average grant date fair value	$ 101.93	$ 90.91	$ 120.99
Total intrinsic value of stock-based awards converted into common shares	$ 3,000,000	$ 2,800,000	$ 3,700,000
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	$ 110.65	$ 110.19	$ 94.54

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Unrecognized cost of unvested share-based compensation awards.

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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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The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

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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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