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Stock-based Compensation (Narrative) (Details) - USD ($)
12 Months Ended
Aug. 31, 2021
Aug. 31, 2020
Aug. 31, 2019
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 543,700    
Allocated share-based compensation expense $ 9,555,000 $ 5,358,000 $ 4,446,000
Employee service share-based, Tax benefit from compensation expense $ 2,000,000.0 1,200,000 1,000,000.0
Restricted Stock Units [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Granted, Number of Shares 17,244    
Allocated share-based compensation expense $ 3,656,000 3,325,000 2,876,000
Employee service share-based, Tax benefit from compensation expense 1,900,000 $ 1,200,000 $ 1,400,000
Compensation cost not yet recognized $ 500,000    
Remaining weighted-average vesting periods 1 year 7 months 6 days    
Weighted-average grant date fair value $ 208.29 $ 184.43 $ 163.93
Total intrinsic value of stock-based awards converted into common shares $ 8,500,000 $ 5,400,000 $ 6,000,000.0
Market Share Units [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Granted, Number of Shares 13,701    
Allocated share-based compensation expense $ 2,294,000 2,033,000 1,570,000
Employee service share-based, Tax benefit from compensation expense 1,300,000 $ 900,000 $ 900,000
Compensation cost not yet recognized $ 2,800,000    
Remaining weighted-average vesting periods 1 year 9 months    
Weighted-average grant date fair value $ 184.96 $ 216.77 $ 177.82
Total intrinsic value of stock-based awards converted into common shares $ 5,900,000 $ 4,400,000 $ 4,000,000.0
Expected volatility period 2 years 10 months 17 days 2 years 10 months 24 days 2 years 10 months 24 days
Percent of original target number of vested shares 100.00%    
Expected dividend yield 0.00% 0.00% 0.00%
Deferred Performance Units [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Granted, Number of Shares 0    
Compensation cost not yet recognized $ 0    
Performance Share Units [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Granted, Number of Shares 19,468    
Allocated share-based compensation expense [1] $ 3,605,000    
Compensation cost not yet recognized $ 0    
Weighted-average grant date fair value $ 197.51    
Vesting percentage 100.00%    
Converted units to common shares 0    
Key Executives [Member] | Restricted Stock Units [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting period 3 years    
High Level Employees [Member] | Restricted Stock Units [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting period 3 years    
High Level Employees [Member] | Market Share Units [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting period 3 years    
Minimum [Member] | Performance Share Units [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting percentage 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] | Performance Share Units [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting percentage 100.00%    
[1] PSU awards, similar to DPU awards that were replaced by PSUs in fiscal year 2021, contain performance conditions for which accrual of expense is based on the probable outcome of the performance conditions. Vesting of DPUs related to the measurement years of both fiscal year 2020 and 2019 was deemed not probable at the end of each fiscal year. DPUs were then discontinued by the Company prior fiscal year 2021. PSUs pertaining to the measurement year of fiscal year 2021 vested at 100% since the performance conditions were fully achieved.