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Income Taxes - Narrative (Details) - USD ($) $ in Thousands | 12 Months Ended
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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 |

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- Definition Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 740 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482685/740-10-50-2 + Details
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