Income Taxes - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Operating Loss Carryforwards [Line Items]
Valuation allowance	$ 448,867	$ 284,626
Income tax expense (benefit) related to uncertain tax positions	(3,300)	$ 0	$ 3,500
Undistributed earnings of foreign subsidiaries	0
Federal
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	223,100
Operating loss carryforwards subject to expiration	23,300
Operating loss carryforwards not subject to expiration	199,800
Income tax credits	85,600
State
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	693,200
Operating loss carryforwards not subject to expiration	5,400
Income tax credits	20,100
Tax credit carryforward, amount, subject to expiration	11,200
Foreign
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	$ 38,300