Debt - Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2024	Mar. 31, 2023
Debt Instrument [Line Items]
(Gain) loss on extinguishment			$ 3,500	$ 0	$ 3,545
Senior Notes | 2029 Convertible Notes
Debt Instrument [Line Items]
Contractual interest expense	$ 2,157	$ 2,156		4,313	2,587
Amortization of deferred financing costs	228	197		472	249
Total interest expense	2,385	2,353		4,785	2,836
Senior Notes | 2025 Convertible Notes
Debt Instrument [Line Items]
Contractual interest expense	614	614		1,228	1,556
Amortization of deferred financing costs	123	120		254	308
(Gain) loss on extinguishment	0	0		0	(5,389)
Total interest expense	737	734		1,482	(3,525)
Senior Notes | 2024 Convertible Notes
Debt Instrument [Line Items]
Contractual interest expense	247	247		494	1,123
Amortization of deferred financing costs	39	41		81	179
(Gain) loss on extinguishment	0	0		0	8,935
Total interest expense	$ 286	$ 288		$ 575	$ 10,237