Summary Of Significant Accounting Policies (Schedule Of Other Accruals And Current Liabilities) (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Sep. 30, 2019
Summary Of Significant Accounting Policies [Line Items]
Regulatory Liabilities	$ 42,598	$ 50,332
Reserve for Gas Replacement	14,356	36,632
Liability for Royalty and Working Interests	12,061	18,057
Other Accruals and Current Liabilities	138,344	139,600
Accrued Capital Expenditures [Member]
Summary Of Significant Accounting Policies [Line Items]
Other	35,645	33,713
Reserve For Gas Replacement [Member]
Summary Of Significant Accounting Policies [Line Items]
Reserve for Gas Replacement	10,622	0
Other Accruals [Member]
Summary Of Significant Accounting Policies [Line Items]
Other	24,065	24,304
Federal [Member]
Summary Of Significant Accounting Policies [Line Items]
Income Taxes Payable	159	0
Non-Qualified [Member] | Current [Member]
Summary Of Significant Accounting Policies [Line Items]
Non-Qualified Benefit Plan Liability	$ 13,194	$ 13,194