Loss per Share - Schedule of Dilutive Securities (Details) - shares	3 Months Ended		6 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Mar. 31, 2026	Mar. 31, 2025
Class B-1 common stock
Loss per Share
Antidilutive securities (in shares)	51,499,195	51,499,195	51,499,195	51,499,195
Shares underlying the conversion option in the 2030 Convertible Senior Notes
Loss per Share
Antidilutive securities (in shares)	18,738,880	18,738,880	18,738,880	18,738,880
Employee Stock Option
Loss per Share
Antidilutive securities (in shares)	1,397,309	2,594,137	1,397,309	2,594,137
Outstanding restricted stock units ("RSUs")
Loss per Share
Antidilutive securities (in shares)	1,770,029	2,772,801	1,770,029	2,772,801
Outstanding restricted stock units ("RSUs") \| Outstanding restricted stock ("Nispera equity")
Loss per Share
Antidilutive securities (in shares)		177,067		177,067
Outstanding performance share units ("PSUs")
Loss per Share
Antidilutive securities (in shares)	979,132	982,820	979,132	982,820
Outstanding non-qualified stock options
Loss per Share
Antidilutive securities (in shares)	657,313	474,992	657,313	474,992