Debt - Interest Expense (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Dec. 31, 2022	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Debt Instrument [Line Items]
Amortization of debt discount		$ 1,561	$ 1,433	$ 13,797
Gain (loss) on extinguishment of debt	$ 3,500	3,545	0	0
Senior Notes | 2029 Convertible Notes
Debt Instrument [Line Items]
Contractual interest expense		6,900	0	0
Amortization of deferred financing costs		742	0	0
Total interest expense		7,642	0	0
Senior Notes | 2025 Convertible Notes
Debt Instrument [Line Items]
Contractual interest expense		2,779	4,097	4,097
Amortization of deferred financing costs		559	797	560
Amortization of debt discount		0	0	6,919
Gain (loss) on extinguishment of debt		(5,389)	0	0
Total interest expense		(2,051)	4,894	11,576
Senior Notes | 2024 Convertible Notes
Debt Instrument [Line Items]
Contractual interest expense		1,609	4,133	4,133
Amortization of deferred financing costs		260	635	446
Amortization of debt discount		0	0	5,903
Gain (loss) on extinguishment of debt		8,935	0	0
Total interest expense		$ 10,804	$ 4,768	$ 10,482