Balance Sheet Accounts - Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Jun. 30, 2025	Sep. 30, 2024
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 455,278	$ 444,053
Less: Accumulated depreciation and amortization	(74,230)	(58,021)
Property, plant and equipment, net	381,048	386,032
Land
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,996	2,996
Buildings
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	249,245	75,988
Research equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	59,561	65,353
Manufacturing equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	16,548	0
Furniture
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	5,594	5,594
Computers and software
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,059	981
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	104,403	104,410
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 15,872	$ 188,731