Debt - Interest Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Debt Instrument [Line Items]
Amortization of debt discount	$ 1,433	$ 13,797	$ 13,200
Senior Notes | 2024 Convertible Notes
Debt Instrument [Line Items]
Contractual interest expense	4,133	4,133	4,133
Amortization of deferred financing costs	635	446	446
Amortization of debt discount	0	5,903	5,437
Total interest expense	4,768	10,482	10,016
Senior Notes | 2025 Convertible Notes
Debt Instrument [Line Items]
Contractual interest expense	4,097	4,097	4,097
Amortization of deferred financing costs	797	560	561
Amortization of debt discount	0	6,919	6,393
Total interest expense	$ 4,894	$ 11,576	$ 11,051