Balance Sheet Accounts - Summary of Property and Equipment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023	Sep. 30, 2023
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 429,814		$ 429,814			$ 332,213
Less: Accumulated depreciation and amortization	(53,903)		(53,903)			(41,951)
Property, plant and equipment, net	375,911		375,911			290,262
Depreciation and amortization expense for property and equipment	4,400	$ 2,900	12,300	$ 7,400
Land
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,996		2,996			2,996
Building
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	75,868		75,868			0
Property, plant and equipment, reclassification			75,900
Useful life					39 years
Research equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	64,207		64,207			56,509
Furniture
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	5,593		5,593			1,540
Computers and software
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	976		976			700
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	104,396		104,396			103,813
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 175,778		175,778			$ 166,655
Property, plant and equipment, reclassification			$ (75,900)