Summary Of Significant Accounting Policies (Schedule Of Other Accruals And Current Liabilities) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Summary Of Significant Accounting Policies [Line Items]
Regulatory Liabilities	$ 55,678	$ 54,349
Liability for Royalty and Working Interests	15,665	18,057
Other Accruals and Current Liabilities	140,176	139,600
Accrued Capital Expenditures [Member]
Summary Of Significant Accounting Policies [Line Items]
Other	33,344	33,713
Regulatory Liabilities [Member]
Summary Of Significant Accounting Policies [Line Items]
Regulatory Liabilities	44,890	50,332
Other Accruals [Member]
Summary Of Significant Accounting Policies [Line Items]
Other	31,654	24,304
Federal [Member]
Summary Of Significant Accounting Policies [Line Items]
Income Taxes Payable	163	0
Non-Qualified [Member]
Summary Of Significant Accounting Policies [Line Items]
Non-Qualified Benefit Plan Liability	98,100	99,500	$ 86,100
Non-Qualified [Member] | Current [Member]
Summary Of Significant Accounting Policies [Line Items]
Non-Qualified Benefit Plan Liability	$ 14,460	$ 13,194	$ 11,500