Details of Selected Financial Statement Captions - Other Current Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Sep. 30, 2023
Balance Sheet Related Disclosures [Abstract]
Customer credit balances and deposits	$ 62,085	$ 65,266
Accrued employee costs	64,141	50,042
Deferred gas costs	9,142	23,093
Operating lease liabilities (See Note 7)	34,340	35,820
Accrued interest	106,116	78,939
Liabilities from risk management activities	7,324	14,584
Taxes payable	215,857	195,468
Pension and postretirement liabilities	4,622	9,375
Regulatory cost of removal obligation	99,217	85,850
APT annual adjustment mechanism	35,924	34,550
Regulatory excess deferred taxes (See Note 15)	79,686	131,301
Other	32,166	38,798
Total	$ 750,620	$ 763,086