Details of Selected Financial Statement Captions - Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Sep. 30, 2023
Balance Sheet Related Disclosures [Abstract]
Storage plant	$ 708,617	$ 668,237
Transmission plant	5,713,831	4,995,579
Distribution plant	17,304,207	15,283,965
General plant	1,019,018	972,054
Intangible plant	38,612	38,612
Property, plant and equipment	24,784,285	21,958,447
Construction in progress	1,063,798	939,927
Total property, plant and equipment and construction in progress	25,848,083	22,898,374
Less: accumulated depreciation and amortization	(3,643,716)	(3,291,791)
Net property, plant and equipment	22,204,367	19,606,583
Plant acquisition adjustments	$ (22,900)	$ (24,800)