Leases - Components of Lease Assets and Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Lease Assets and Liabilities
Right-of-use assets	$ 45,255	$ 45,297
Lease liabilities	6,342	10,563
Lease liabilities, net of current portion	111,027	104,608
Lease Cost
Total	16,689	13,259	$ 9,763
Research and development
Lease Cost
Operating lease cost	11,035	10,350	7,278
Variable lease cost	3,648	1,179	728
General and administrative expense
Lease Cost
Operating lease cost	2,006	1,730	1,757
Variable lease cost	$ 0	$ 0	$ 0