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Employee and Retiree Benefits (Deferred Compensation Narrative) (Details) - USD ($)
$ in Millions
 12 Months Ended
Aug. 26, 2017
Aug. 27, 2016
Aug. 29, 2015
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Employer discretionary contribution amount $ 1.6 $ 1.5 $ 1.2
Key Employees [Member] | Non-Qualified Deferred Compensation Program (1981) [Member]      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Vesting age 55 years    
Requisite service period 5 years    
Requiste service period prior to December 1992 20 years    
Deferred compensation expense $ 1.2 1.3 $ 1.3
Deferred compensation liabilities 16.5 18.0  
Officers and Managers [Member] | Supplemental Employee Retirement Plan (SERP) [Member]      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Deferred compensation liabilities $ 2.5 2.7  
Contractual amount of years after retirement 15 years    
Non-Qualified Share Option Program (2001) [Member]      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Deferred compensation assets $ 1.6 3.7  
Deferred share-based compensation liabilities $ 1.5 3.3  
Additional contribution at initiation 25.00%    
Required option exercise period 15 years    
Executive Deferred Compensation Plan 2007 [Member] | Officers and Key Employees [Member]      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Deferred compensation liabilities $ 0.4 0.4  
Deferred compensation assets $ 0.4 $ 0.4  
Maximum salary deferral 50.00%    
Maximum cash incentive award deferral 100.00%