Leases - Schedule of Components of Lease Assets and Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Mar. 31, 2025	Mar. 31, 2024	Mar. 31, 2025	Mar. 31, 2024	Sep. 30, 2024
Lease Assets and Liabilities
Right-of-use assets	$ 44,452		$ 44,452		$ 45,255
Lease liabilities	6,782		6,782		6,342
Lease liabilities, net of current portion	107,529		107,529		$ 111,027
Lease Cost
Total	4,160	$ 3,899	8,450	$ 8,148
Research and development
Lease Cost
Operating lease cost	2,709	2,572	5,520	5,566
Variable lease cost	951	836	1,937	1,615
General and administrative expense
Lease Cost
Operating lease cost	500	491	993	967
Variable lease cost	$ 0	$ 0	$ 0	$ 0

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Amount of lease cost recognized by lessee for lease contract.

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Amount of single lease cost, calculated by allocation of remaining cost of lease over remaining lease term. Includes, but is not limited to, single lease cost, after impairment of right-of-use asset, calculated by amortization of remaining right-of-use asset and accretion of lease liability.

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Present value of lessee's discounted obligation for lease payments from operating lease, classified as current.

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Present value of lessee's discounted obligation for lease payments from operating lease, classified as noncurrent.

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Amount of lessee's right to use underlying asset under operating lease.

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Amount of variable lease cost, excluded from lease liability, recognized when obligation for payment is incurred for finance and operating leases.

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