Stock-Based Compensation - Expenses Included in Operating Expenses (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	$ 14,711	$ 19,947	$ 48,984	$ 59,949
Research and development
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	6,221	8,982	21,634	26,129
General and administrative expense
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	$ 8,490	$ 10,965	$ 27,350	$ 33,820