Leases - Components of Lease Assets and Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Sep. 30, 2022
Lease Assets and Liabilities
Right-of-use assets	$ 40,667		$ 40,667		$ 58,291
Lease liabilities	2,823		2,823		2,776
Lease liabilities, net of current portion	79,911		79,911		$ 78,800
Lease Cost
Total	4,089	$ 3,601	9,904	$ 6,564
Research and development
Lease Cost
Operating lease cost	3,323	2,974	7,735	4,757
Variable lease cost (1)	257	179	627	519
General and administrative expense
Lease Cost
Operating lease cost	509	448	1,542	1,288
Variable lease cost (1)	$ 0	$ 0	$ 0	$ 0