Details of Selected Financial Statement Captions - Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Sep. 30, 2022
Balance Sheet Related Disclosures [Abstract]
Storage plant	$ 668,237	$ 589,210
Transmission plant	4,995,579	4,325,540
Distribution plant	15,283,965	13,511,409
General plant	972,054	937,500
Intangible plant	38,612	38,612
Property, plant and equipment	21,958,447	19,402,271
Construction in progress	939,927	835,868
Total property, plant and equipment and construction in progress	22,898,374	20,238,139
Less: accumulated depreciation and amortization	(3,291,791)	(2,997,900)
Net property, plant and equipment	19,606,583	17,240,239
Plant acquisition adjustments	$ (24,800)	$ (26,600)