Derivative Instruments and Hedging Activities (Summary Of Balance Sheet Locations And Related Fair Values Of Outstanding Derivative Instruments) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Derivatives, Fair Value [Line Items]
Derivative Assets, Fair Value, Net Asset	$ 54,869	$ 8,642
Derivative Liability, Fair Value, Net Liability	25,897	52,420
Prepayments and other
Derivatives, Fair Value [Line Items]
Derivative Assets, Fair Value, Net Asset	53,850	6,972
Accrued Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Net Liability		26,843
Other Intangible Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets, Fair Value, Net Asset	1,019	1,670
Other Long Term Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Net Liability	25,897	25,577
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	35,249	6,972
Derivative Asset, Fair Value, Gross Liability	(12,942)	0
Derivative Liability, Fair Value, Gross Liability	20,398	23,335
Derivative Liability, Fair Value, Gross Asset	(17,007)	(12,611)
Derivative Assets, Fair Value, Net Asset	22,307	6,972
Derivative Liability, Fair Value, Net Liability	3,391	10,724
Not Designated as Hedging Instrument [Member] | Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	17,630	6,972
Derivative Asset, Fair Value, Gross Liability	(12,942)	0
Derivative Liability, Fair Value, Gross Liability	20,398	19,766
Derivative Liability, Fair Value, Gross Asset	(17,007)	(12,611)
Derivative Assets, Fair Value, Net Asset	4,688	6,972
Derivative Liability, Fair Value, Net Liability	3,391	7,155
Not Designated as Hedging Instrument [Member] | Nymex Futures Contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	17,619	0
Derivative Asset, Fair Value, Gross Liability	0	0
Derivative Liability, Fair Value, Gross Liability		3,569
Derivative Liability, Fair Value, Gross Asset		0
Derivative Assets, Fair Value, Net Asset	17,619	0
Derivative Liability, Fair Value, Net Liability		3,569
Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	174,677	1,670
Derivative Asset, Fair Value, Gross Liability	(142,115)	0
Derivative Liability, Fair Value, Gross Liability	22,506	65,375
Derivative Liability, Fair Value, Gross Asset	0	(23,679)
Derivative Assets, Fair Value, Net Asset	32,562	1,670
Derivative Liability, Fair Value, Net Liability	22,506	41,696
Designated as Hedging Instrument [Member] | Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	173,658	0
Derivative Asset, Fair Value, Gross Liability	(142,115)	0
Derivative Liability, Fair Value, Gross Liability	21,441	63,561
Derivative Liability, Fair Value, Gross Asset	0	(23,679)
Derivative Assets, Fair Value, Net Asset	31,543	0
Derivative Liability, Fair Value, Net Liability	21,441	39,882
Designated as Hedging Instrument [Member] | Interest rate swap
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	1,019	1,670
Derivative Asset, Fair Value, Gross Liability	0	0
Derivative Liability, Fair Value, Gross Liability	1,065	1,814
Derivative Liability, Fair Value, Gross Asset	0	0
Derivative Assets, Fair Value, Net Asset	1,019	1,670
Derivative Liability, Fair Value, Net Liability	$ 1,065	$ 1,814