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Details of Selected Financial Statement Captions - Deferred Charges and Other Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Sep. 30, 2024
Balance Sheet Related Disclosures [Abstract]
Marketable securities	$ 114,938	$ 110,594
Regulatory assets (See Note 3)	428,951	396,958
Operating lease right of use assets (See Note 7)	293,934	249,556
Winter Storm Uri incremental costs	0	6,424
Assets from risk management activities	4,594	94,197
Pension and postretirement assets	226,409	155,611
Other	28,627	30,343
Total	$ 1,097,453	$ 1,043,683

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