Deferred Tax Assets, Operating Loss Carryforwards, Domestic Impact, State And Local

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Deferred Tax Liability, Regulatory Excess, Return Term

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Amount of federal tax effects on state operating loss carryforward available to reduce future taxable income under enacted tax laws.

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Unrecognized Tax Benefits, Deferred Tax Liabilities

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible charitable contribution carryforwards.

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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482685/740-10-50-6

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Amount, after deferred tax asset, of deferred tax liability attributable to taxable differences without jurisdictional netting.

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-SubTopic 10
-Name Accounting Standards Codification
-Section 50
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-URI https://asc.fasb.org/1943274/2147482685/740-10-50-2

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Amount of deferred tax liability attributable to taxable temporary differences from regulatory assets.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount of operating loss carryforward, before tax effects, available to reduce future taxable income under enacted tax laws.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-SubTopic 10
-Name Accounting Standards Codification
-Section 50
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The amount for the individual regulatory liability as itemized in a table of regulatory liabilities as of the end of the period.

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The amount of the tax credit carryforward, before tax effects, available to reduce future taxable income under enacted tax laws.

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Amount accrued for interest on an underpayment of income taxes and penalties related to a tax position claimed or expected to be claimed in the tax return.

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Amount of expense for interest on an underpayment of income taxes and penalties related to a tax position claimed or expected to be claimed in the tax return.

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Amount of increase (decrease) in unrecognized tax benefits attributable to uncertain tax positions taken in tax returns.

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Income Taxes - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
Income Taxes - Narrative (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Income Tax Contingency [Line Items]
Charitable contribution carryforwards	$ 11,800
Remeasured federal effects	600
Unrecognized tax benefits, period increase	60,300	$ 57,800
Unrecognized tax benefits, deferred tax liabilities	10,100	11,600
Interest and penalties	100	100	$ 3,400
Payment of interest and penalties accrued	15,100	15,100	$ 15,100
Regulatory liabilities	1,269,648	1,227,882
Regulatory excess net deferred tax liability	140,500
Deferred tax liabilities, net	2,918,347	2,593,342
Regulatory excess deferred taxes
Income Tax Contingency [Line Items]
Regulatory liabilities	190,274	257,001
Regulatory excess deferred taxes to be returned tranche one
Income Tax Contingency [Line Items]
Deferred tax liabilities, net	$ 91,800
Regulatory excess deferred taxes to be returned tranche one \| Minimum
Income Tax Contingency [Line Items]
Return basis, term	36 months
Regulatory excess deferred taxes to be returned tranche one \| Maximum
Income Tax Contingency [Line Items]
Return basis, term	60 months
Regulatory excess deferred taxes to be returned tranche two
Income Tax Contingency [Line Items]
Regulatory liabilities	$ 47,700
Regulatory excess deferred taxes to be returned tranche two \| Minimum
Income Tax Contingency [Line Items]
Return basis, term	15 years
Regulatory excess deferred taxes to be returned tranche two \| Maximum
Income Tax Contingency [Line Items]
Return basis, term	69 years
Regulatory excess deferred taxes to be returned tranche three
Income Tax Contingency [Line Items]
Deferred tax liabilities, net	$ 1,000
Other current liabilities \| Regulatory excess deferred taxes
Income Tax Contingency [Line Items]
Regulatory liabilities	72,800	$ 79,700
Domestic Tax Jurisdiction
Income Tax Contingency [Line Items]
Federal net operating loss carryforwards	435,300
State and Local Jurisdiction
Income Tax Contingency [Line Items]
Federal net operating loss carryforwards	38,300
Federal effects	10,100
Federal alternative minimum tax credit carryforwards	$ 2,400