Details of Selected Financial Statement Captions - Other Non-Operating Income (Details) - USD ($) $ in Thousands	12 Months Ended
Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Balance Sheet Related Disclosures [Abstract]
Equity component of AFUDC	$ 75,425	$ 58,234	$ 64,019
Performance-based rate program	8,485	8,389	7,093
Pension and other postretirement non-service credit	14,372	10,820	8,955
Interest income	29,944	22,887	7,207
Community support spending	(21,114)	(20,016)	(12,027)
Unrealized gains on equity securities	174	3,562	1,406
Miscellaneous	(17,545)	(12,830)	(6,878)
Total	$ 89,741	$ 71,046	$ 69,775

Charitable Contributions

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- Definition

Miscellaneous Non Operating Income (Expense)

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- Definition

Non-service costs related to our pension and other postretirement plans recorded in other non-operating income (expense)

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No definition available.

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- Definition

Performance-based Rate Program Income (Loss)

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- Definition

Amount of unrealized gain (loss) on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Amount of interest income (expense) classified as nonoperating.

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Amount of income (expense) related to nonoperating activities, classified as other.

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- Definition

The component of the allowance for funds used during construction during the period based on an assumed rate of return on equity funds used in financing the construction of regulated assets.

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