Details of Selected Financial Statement Captions - Other Current Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Sep. 30, 2022
Balance Sheet Related Disclosures [Abstract]
Customer credit balances and deposits	$ 65,266	$ 56,016
Accrued employee costs	50,042	47,661
Deferred gas costs	23,093	28,834
Operating lease liabilities (See Note 7)	35,820	38,644
Accrued interest	78,939	59,542
Liabilities from risk management activities	14,584	3,000
Taxes payable	195,468	189,239
Pension and postretirement liabilities	9,375	9,721
Regulatory cost of removal obligation	85,850	80,676
APT annual adjustment mechanism	34,550	18,034
Regulatory excess deferred taxes (See Note 15)	131,301	159,808
Other	38,798	28,982
Total	$ 763,086	$ 720,157