Derivatives And Risk Management Derivatives and Risk Management (Collateral) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Derivative [Line Items]
Derivative, Fair Value, Amount Offset Against Collateral, Net	$ 44,758	$ 48,556
Commodity Contract [Member]
Derivative [Line Items]
Liability position at aggregate fair value	1,124	7,090
Collateral Already Posted, Aggregate Fair Value	17,134	28,716
Letters of credit outstanding	24,400	28,200
Derivative, Fair Value, Amount Offset Against Collateral, Net	9,858	14,526
Additional Collateral, Aggregate Fair Value	1,046	6,980
Interest Rate Swap [Member]
Derivative [Line Items]
Liability position at aggregate fair value	73,978	85,498
Collateral Already Posted, Aggregate Fair Value	34,900	34,030
Letters of credit outstanding	3,600	9,600
Derivative, Fair Value, Amount Offset Against Collateral, Net	34,900	34,030
Additional Collateral, Aggregate Fair Value	$ 21,100	$ 18,750