Stock Based Compensation - Valuation Assumptions for an Employee Stock Purchase Plan (Details) - Employee Stock	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate (as a percent)	5.20%	1.70%	0.30%
Volatility (as a percent)	57.00%	49.00%	53.00%
Expected life	6 months	6 months	6 months
Dividend yield (as a percent)			0.60%