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Summary Of Significant Accounting Policies (Components Of Other Current Assets) (Details) - USD ($)
$ in Thousands
Dec. 31, 2017
Sep. 30, 2017
Summary Of Significant Accounting Policies [Line Items]    
Prepayments $ 7,259 $ 10,927
Prepaid Property and Other Taxes 14,972 13,974
Fair Values of Firm Commitments 3,218 1,031
Regulatory Assets 13,301 15,884
Other Current Assets 47,914 51,505
State [Member]    
Summary Of Significant Accounting Policies [Line Items]    
Income Taxes Receivable $ 9,164 $ 9,689