Summary Of Significant Accounting Policies (Schedule Of Other Accruals And Current Liabilities) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Summary Of Significant Accounting Policies [Line Items]
Regulatory Liabilities	$ 60,881	$ 55,678
Liability for Royalty and Working Interests	31,483	15,665
Other Accruals and Current Liabilities	194,169	140,176
Accrued Capital Expenditures [Member]
Summary Of Significant Accounting Policies [Line Items]
Other	42,541	33,344
Regulatory Liabilities [Member]
Summary Of Significant Accounting Policies [Line Items]
Regulatory Liabilities	60,860	44,890
Other Accruals [Member]
Summary Of Significant Accounting Policies [Line Items]
Other	43,723	31,654
Federal [Member]
Summary Of Significant Accounting Policies [Line Items]
Income Taxes Payable	154	163
Non-Qualified [Member]
Summary Of Significant Accounting Policies [Line Items]
Non-Qualified Benefit Plan Liability	95,800	98,100	$ 99,500
Non-Qualified [Member] | Current [Member]
Summary Of Significant Accounting Policies [Line Items]
Non-Qualified Benefit Plan Liability	$ 15,408	$ 14,460	$ 13,200