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Summary Of Significant Accounting Policies (Components Of Other Current Assets) (Details) - USD ($)
$ in Thousands
Dec. 31, 2019
Sep. 30, 2019
Summary Of Significant Accounting Policies [Line Items]    
Prepayments $ 9,135 $ 12,728
Prepaid Property and Other Taxes 15,340 14,361
Fair Values of Firm Commitments 9,803 7,538
Regulatory Assets 14,588 11,460
Other Current Assets 96,831 97,054
State [Member]    
Summary Of Significant Accounting Policies [Line Items]    
Income Taxes Receivable 5,576 8,579
Other Current Assets [Member] | Federal [Member]    
Summary Of Significant Accounting Policies [Line Items]    
Income Taxes Receivable $ 42,389 $ 42,388