Derivatives And Risk Management (Narrative) (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Derivative [Line Items]
Derivative, Fair Value, Amount Offset Against Collateral, Net	$ 51,337	$ 44,758
Commodity Contracts [Member]
Derivative [Line Items]
Cash deposited as collateral	15,924	17,134
Letters of credit outstanding	37,250	24,400
Derivative, Fair Value, Amount Offset Against Collateral, Net	9,767	9,858
Liability position at aggregate fair value	648	1,124
Additional Collateral, Aggregate Fair Value	648	1,046
Interest Rate Swap [Member]
Derivative [Line Items]
Cash deposited as collateral	41,570	34,900
Letters of credit outstanding	13,100	3,600
Derivative, Fair Value, Amount Offset Against Collateral, Net	41,570	34,900
Liability position at aggregate fair value	80,266	73,978
Additional Collateral, Aggregate Fair Value	$ 11,210	$ 21,100