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Amount of annual reduction to the corporate income tax rate.

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Income Taxes [Line Items]

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Increase to Taxes Refundable to Customers Impact of Changes in Corporate Tax Rate

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Regulatory assets representing future amounts collectible from customers corresponding to additional deferred income taxes not previously recorded because of ratemaking practices.

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Reduction in Deferred Taxes Rate Regulated Activities Impact of Change in Corporate Tax Rate

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Noncurrent regulatory liability representing the reduction of previously recorded deferred income taxes associated with rate-regulated activities that are expected to be refundable to customers as of the end of the period.

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations applicable to state and local income tax expense (benefit), net of federal tax expense (benefit).

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Amount of income tax expense (benefit) from continuing operations attributable to an adjustment of a deferred tax liability or asset for enacted changes in tax laws or rates or a change in the tax status of the entity.

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Amount of unrecognized tax benefits.

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Amount of increase (decrease) in the valuation allowance for a specified deferred tax asset.

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Income Taxes - Narrative (Details) - USD ($)			3 Months Ended	12 Months Ended
Income Taxes - Narrative (Details) - USD ($)	Sep. 30, 2022	Jun. 30, 2022	Sep. 30, 2022	Sep. 30, 2032	Sep. 30, 2024	Sep. 30, 2022	Oct. 01, 2024	Sep. 30, 2023
Income Taxes [Line Items]
Taxes refundable to customers					$ 305,645,000			$ 268,562,000
Recoverable future taxes					80,084,000			69,045,000
Unrecognized tax benefits	$ 0		$ 0		0	$ 0		0
Sale of California Assets
Income Taxes [Line Items]
Adjustments to valuation allowance		$ (27,200,000)
Pennsylvania Tax Rate Change
Income Taxes [Line Items]
Adjustments to valuation allowance			(5,500,000)
Remaining State Deferred Tax Assets
Income Taxes [Line Items]
Adjustments to valuation allowance	$ (24,900,000)
Deferred Income Taxes
Income Taxes [Line Items]
Taxes refundable to customers					305,600,000			268,600,000
Recoverable future taxes					$ 80,100,000			$ 69,000,000.0
Pennsylvania
Income Taxes [Line Items]
Corporate income tax rate					8.99%
Increase (decrease) in deferred income taxes						$ (28,400,000)
Reduction in deferred taxes for rate regulated activities due to remeasurement of deferred income tax assets and liabilities			37,200,000
Pennsylvania \| Taxes Refundable to Customers
Income Taxes [Line Items]
Increase to taxes refundable to customers, impact of changes in corporate tax rate			17,400,000
Pennsylvania \| Recoverable Future Taxes
Income Taxes [Line Items]
Decrease to recoverable future taxes, impact of change in corporate tax rate			$ 19,800,000
Pennsylvania \| Forecast
Income Taxes [Line Items]
Corporate income tax rate				4.99%
Annual reduction in corporate income tax Rate from fiscal 2025 to fiscal 2032 (as a percent)							0.50%