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Employee Benefit Plans Employee Benefit Plans - Employee Stock Purchase Plan, Incentive Bonus Plan and Stock-Based Compensation (Details) - USD ($)
 12 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Discounted Price For Purchasing Company's Common Stock 85.00%    
Employee Stock Purchase Plan, Maximum Percent of Annual Compensation 15.00%    
Fair Market Value Of Common Stock Available For Purchase To Eligible Employees Maximum $ 25,000    
Stock Issued During Period, Shares, Employee Stock Purchase Plans 111,527 89,652 82,446
Stock Issued During Period, Value, Employee Stock Purchase Plan $ 2,800,000 $ 2,200,000 $ 1,700,000
Officers' Compensation $ 16,800,000 $ 14,200,000 $ 11,800,000
Shares available for grant 19,000,000    
Employee Stock [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Common stock reserved for future issuance, shares 3,200,000    
Stock Compensation Plan [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Common stock reserved for future issuance, shares 31,800,000