Summary Of Significant Accounting Policies (Schedule Of Other Accruals And Current Liabilities) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Sep. 30, 2020
Summary Of Significant Accounting Policies [Line Items]
Regulatory Liabilities	$ 34,832	$ 44,890
Reserve for Gas Replacement	5,745	33,338
Liability for Royalty and Working Interests	22,475	15,665
Other Accruals and Current Liabilities	176,940	140,176
Accrued Capital Expenditures [Member]
Summary Of Significant Accounting Policies [Line Items]
Other	49,526	33,344
Reserve For Gas Replacement [Member]
Summary Of Significant Accounting Policies [Line Items]
Reserve for Gas Replacement	21,432	0
Other Accruals [Member]
Summary Of Significant Accounting Policies [Line Items]
Other	34,215	31,817
Non-Qualified [Member] | Current [Member]
Summary Of Significant Accounting Policies [Line Items]
Non-Qualified Benefit Plan Liability	$ 14,460	$ 14,460