Leases - Components of Lease Assets and Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Sep. 30, 2023
Lease Assets and Liabilities
Right-of-use assets	$ 44,907		$ 45,297
Lease liabilities	3,421		10,563
Lease liabilities, net of current portion	115,157		$ 104,608
Lease Cost
Total	4,249	$ 2,812
Research and development
Lease Cost
Operating lease cost	2,994	2,069
Variable lease cost	779	210
General and administrative expense
Lease Cost
Operating lease cost	476	533
Variable lease cost	$ 0	$ 0