Income Taxes - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024
Operating Loss Carryforwards [Line Items]
Valuation allowance	$ 497,543	$ 448,867
Income tax expense (benefit) related to uncertain tax positions	0	$ 3,300
Federal
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	20,600
Operating loss carryforwards subject to expiration	20,600
Income tax credits	49,400
State
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	815,500
Operating loss carryforwards not subject to expiration	2,700
Income tax credits	26,300
Tax credit carryforward, amount, subject to expiration	13,600
Foreign
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	$ 46,300