Derivative Instruments and Hedging Activities (Summary Of Balance Sheet Locations And Related Fair Values Of Outstanding Derivative Instruments) (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Derivatives, Fair Value [Line Items]
Derivative, Fair Value, Net	$ 3,773	$ 54,869
Derivative Liability, Fair Value, Net Liability	61,947	25,897
Prepayments and other
Derivatives, Fair Value [Line Items]
Derivative, Fair Value, Net	3,469	53,850
Accrued Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Net Liability	36,976
Other Intangible Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative, Fair Value, Net	304	1,019
Other Long Term Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Net Liability	24,971	25,897
Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	304	174,677
Derivative Asset, Fair Value, Gross Liability	0	(142,115)
Derivative, Fair Value, Net	304	32,562
Derivative Liability, Fair Value, Gross Liability	38,869	22,506
Derivative Liability, Fair Value, Gross Asset	0	0
Derivative Liability, Fair Value, Net Liability	38,869	22,506
Designated as Hedging Instrument [Member] | Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	0	173,658
Derivative Asset, Fair Value, Gross Liability	0	(142,115)
Derivative, Fair Value, Net	0	31,543
Derivative Liability, Fair Value, Gross Liability	38,755	21,441
Derivative Liability, Fair Value, Gross Asset	0	0
Derivative Liability, Fair Value, Net Liability	38,755	21,441
Designated as Hedging Instrument [Member] | Interest rate swap
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	304	1,019
Derivative Asset, Fair Value, Gross Liability	0	0
Derivative, Fair Value, Net	304	1,019
Derivative Liability, Fair Value, Gross Liability	114	1,065
Derivative Liability, Fair Value, Gross Asset	0	0
Derivative Liability, Fair Value, Net Liability	114	1,065
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	3,469	35,249
Derivative Asset, Fair Value, Gross Liability	0	(12,942)
Derivative, Fair Value, Net	3,469	22,307
Derivative Liability, Fair Value, Gross Liability	60,196	20,398
Derivative Liability, Fair Value, Gross Asset	(37,118)	17,007
Derivative Liability, Fair Value, Net Liability	23,078	3,391
Not Designated as Hedging Instrument [Member] | Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	0	17,630
Derivative Asset, Fair Value, Gross Liability	0	(12,942)
Derivative, Fair Value, Net	0	4,688
Derivative Liability, Fair Value, Gross Liability	60,196	20,398
Derivative Liability, Fair Value, Gross Asset	(37,118)	17,007
Derivative Liability, Fair Value, Net Liability	23,078	3,391
Not Designated as Hedging Instrument [Member] | Nymex Futures Contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	3,469	17,619
Derivative Asset, Fair Value, Gross Liability	0	0
Derivative, Fair Value, Net	$ 3,469	17,619
Derivative Liability, Fair Value, Gross Liability		0
Derivative Liability, Fair Value, Gross Asset		0
Derivative Liability, Fair Value, Net Liability		$ 0