Long-Term Debt - Schedule of Interest Expense Related to Notes (Details) - 2028 and 2025 Notes - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Debt Instrument [Line Items]
Contractual interest expense	$ 5,383	$ 5,246	$ 5,246
Amortization of debt discount	258	3,755	3,527
Amortization of issuance costs	2,119	944	887
Total interest expense related to the Notes	$ 7,760	$ 9,945	$ 9,660