Collaboration and License Agreements - Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Disaggregation of Revenue [Line Items]
Revenue	$ 829,448	$ 3,551	$ 240,735
GSK
Disaggregation of Revenue [Line Items]
Revenue	2,645	2,685	29,657
Horizon
Disaggregation of Revenue [Line Items]
Revenue	0	0	23,206
Takeda
Disaggregation of Revenue [Line Items]
Revenue	0	866	162,516
Janssen
Disaggregation of Revenue [Line Items]
Revenue	0	0	356
Amgen
Disaggregation of Revenue [Line Items]
Revenue	0	0	25,000
Sarepta
Disaggregation of Revenue [Line Items]
Revenue	696,803	0	0
Sanofi
Disaggregation of Revenue [Line Items]
Revenue	$ 130,000	$ 0	$ 0