Balance Sheet Accounts - Summary of Property and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2023
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 444,053	$ 332,213
Less: Accumulated depreciation and amortization	(58,021)	(41,951)
Property, plant and equipment, net	386,032	290,262
Depreciation and amortization expense for property and equipment	16,900	10,700	$ 8,700
Land
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,996	2,996
Building
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	75,988	0
Property, plant and equipment, reclassification	$ 76,000
Estimated Useful Lives	39 years			39 years
Research equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 65,353	56,509
Furniture
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 5,594	1,540
Estimated Useful Lives	7 years
Computers and software
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 981	700
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	104,410	103,813
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	188,731	$ 166,655
Property, plant and equipment, reclassification	$ (76,000)