Employee Benefit Plans Employee Benefit Plans - Employee Stock Purchase Plan, Incentive Bonus Plan and Stock-Based Compensation (Details) - USD ($)	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
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	131,348	141,661	114,340
Stock Issued During Period, Value, Employee Stock Purchase Plan	$ 5,600,000	$ 4,600,000	$ 4,000,000.0
Salary and Wage, Officer, Excluding Cost of Good and Service Sold	$ 34,300,000	$ 24,400,000	$ 23,700,000
Shares available for grant	9,400,000
Employee Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance, shares	2,800,000
Share-based Payment Arrangement [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance, shares	16,400,000