Stock-Based Compensation - Expenses Included in Operating Expenses (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock compensation	$ 54,848	$ 67,097	$ 78,130
Research and development
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock compensation	27,320	29,527	34,332
General and administrative expense
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock compensation	$ 27,528	$ 37,570	$ 43,798