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Employee Stock Purchase and Stock Option Plans (Stock Issuance Activity Under the 1989 ESPP and the GESPP) (Details) - USD ($)
 12 Months Ended
Jan. 19, 2017
Sep. 29, 2017
Sep. 30, 2016
Oct. 02, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Discount (percent) available to employees on the purchase of common stock   5.00%    
Aggregate Purchase Price Paid for Shares Sold   $ 23,190,491 $ 26,291,308 $ 32,157,279
Aggregate Number of Shares Sold   443,300 627,657 781,214
Shares reserved for future Issuance (in shares)   10,181,183    
Under the 1989 ESPP        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Aggregate Purchase Price Paid for Shares Sold   $ 21,084,657 $ 23,631,241 $ 28,621,800
Aggregate Number of Shares Sold   403,652 564,461 696,853
Increase in number of shares authorized 4,350,000      
Shares reserved for future Issuance (in shares)   4,545,854    
Under the GESPP        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Aggregate Purchase Price Paid for Shares Sold   $ 2,105,834 $ 2,660,067 $ 3,535,479
Aggregate Number of Shares Sold   39,648 63,196 84,361
Increase in number of shares authorized 150,000      
Shares reserved for future Issuance (in shares)   174,980