Derivatives And Risk Management (Narrative) (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Derivative, Fair Value, Amount Offset Against Collateral, Net	$ 43,683	$ 44,758
Commodity Contracts [Member]
Derivative [Line Items]
Cash deposited as collateral	18,514	17,134
Letters of credit outstanding	30,900	24,400
Derivative, Fair Value, Amount Offset Against Collateral, Net	7,543	9,858
Liability position at aggregate fair value	771	1,124
Additional Collateral, Aggregate Fair Value	771	1,046
Interest Rate Swap [Member]
Derivative [Line Items]
Cash deposited as collateral	36,140	34,900
Letters of credit outstanding	4,800	3,600
Derivative, Fair Value, Amount Offset Against Collateral, Net	36,140	34,900
Liability position at aggregate fair value	69,446	73,978
Additional Collateral, Aggregate Fair Value	$ 13,310	$ 21,100