Derivatives (Schedule Of Fair Value Of Derivative Assets And Liabilities) (Details) - Other Current Assets [Member] - Total Commodity Derivatives [Member] - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Not Designated As Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 477	$ 443
Derivative Asset, Fair Value, Gross Liability	(477)	(443)
Derivative Asset	0	0
Derivative Liability, Fair Value, Gross Liability	(1,267)	(1,772)
Derivative Liability, Fair Value, Gross Asset	1,267	1,772
Derivative Liability	0	0
Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	1,431	3,321
Derivative Asset, Fair Value, Gross Liability	(931)	(3,321)
Derivative Asset	500	0
Derivative Liability, Fair Value, Gross Liability	(931)	(9,506)
Derivative Liability, Fair Value, Gross Asset	931	7,589
Derivative Liability	$ 0	$ (1,917)