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Derivatives And Risk Management (Narrative) (Details) - USD ($)
$ in Thousands
Sep. 30, 2019
Dec. 31, 2018
Derivative [Line Items]    
Derivative, Fair Value, Amount Offset Against Collateral, Net $ 12,385 $ 51,747
Commodity Contracts [Member]    
Derivative [Line Items]    
Cash deposited as collateral 4,906 78,025
Letters of credit outstanding 9,500 6,500
Derivative, Fair Value, Amount Offset Against Collateral, Net 3,505 51,217
Liability position at aggregate fair value 1,345 2,193
Additional Collateral, Aggregate Fair Value 1,339 2,193
Interest Rate Swap [Member]    
Derivative [Line Items]    
Cash deposited as collateral 8,880 530
Derivative, Fair Value, Amount Offset Against Collateral, Net 8,880 530
Liability position at aggregate fair value 53,271 7,831
Additional Collateral, Aggregate Fair Value $ 44,391 $ 6,579