Balance Sheet Accounts - Summary of Property and Equipment (Detail) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Sep. 30, 2023
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 379,200		$ 332,213
Less: Accumulated depreciation and amortization	(45,789)		(41,951)
Property, plant and equipment, net	333,411		290,262
Depreciation and amortization expense for property and equipment	3,800	$ 2,300
Land
Property, Plant and Equipment [Line Items]
Property and equipment, gross	2,996		2,996
Building
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 71,797		0
Useful life	39 years
Research equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 59,956		56,509
Furniture
Property, Plant and Equipment [Line Items]
Property and equipment, gross	2,761		1,540
Computers and software
Property, Plant and Equipment [Line Items]
Property and equipment, gross	883		700
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	103,893		103,813
Construction in progress
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 136,914		$ 166,655