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Derivatives And Risk Management Derivatives and Risk Management (Collateral) (Details) - USD ($)
$ in Thousands
Jun. 30, 2018
Dec. 31, 2017
Derivative [Line Items]    
Derivative, Fair Value, Amount Offset Against Collateral, Net $ 22,371 $ 62,408
Commodity Contracts [Member]    
Derivative [Line Items]    
Liability position at aggregate fair value 1,529 1,336
Additional Collateral, Aggregate Fair Value 1,529 1,336
Collateral Already Posted, Aggregate Fair Value 29,757 39,458
Letters of credit outstanding 21,700 23,000
Derivative, Fair Value, Amount Offset Against Collateral, Net 21,781 27,438
Foreign Exchange Contract [Member]    
Derivative [Line Items]    
Collateral Already Posted, Aggregate Fair Value 0 0
Letters of credit outstanding $ 0 $ 0