Derivative Instruments And Hedging Activities (Summary Of Balance Sheet Locations And Related Fair Values Of Outstanding Derivative Instruments) (Details) (USD $)	9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 53,017,000
Derivative Instruments Not Designated as Hedging Instruments, Loss	0
Cash Flow Hedge Derivative Instrument Assets at Fair Value	0	(17,383,000)
Derivative Instrument Not Designated as Hedging Instrument in Asset Position - Asset	815,000
Cash Flow Hedge Derivative Instrument Liabilities at Fair Value	18,700,000	23,875,000
Derivative Instrument not Designated as Hedging Instrument Asset Position - Gross Asset	8,391,000
Derivative Instrument not Designated as Hedging Instrument Asset Position - Liability	(1,934,000)
Cash Flow Hedge Derivative Instrument Liabilities at Fair Value - Gross Liability	18,700,000	41,258,000
Derivative Liability, Fair Value, Gross Liability	(7,207,000)
Interest Rate Cash Flow Hedge Liability at Fair Value	0
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	(10,230,000)
Variable-to-fixed interest rate swap contract, Offsetting Amount	(20,500,000)
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	18,008,000	51,717,000
Derivative Assets	46,625,000
Derivative Liabilities, Current	12,779,000	62,388,000
Derivative Liabilities, Noncurrent	23,929,000	13,204,000
Derivative Liabilities	36,708,000	75,592,000
Commodity Contract [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	51,593,000
Derivative Instrument Not Designated as Hedging Instrument - Gross Liability	28,238,000	46,154,000
Cash Flow Hedge Derivative Instrument Assets at Fair Value	0	(17,383,000)
Derivative, Fair Value, Net	44,386,000
Derivative Instrument Not Designated as Hedging Instrument in Asset Position - Asset	(4,656,000)
Cash Flow Hedge Derivative Instrument Liabilities at Fair Value	16,724,000	20,445,000
Derivative Instrument not Designated as Hedging Instrument Asset Position - Gross Asset	986,000
Derivative Instrument not Designated as Hedging Instrument Asset Position - Liability	(5,642,000)
Cash Flow Hedge Derivative Instrument Liabilities at Fair Value - Gross Liability	16,724,000	37,828,000
Derivative Liability, Fair Value, Gross Liability	(7,207,000)
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	(10,230,000)
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	18,008,000	46,154,000
Interest Rate Swap [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	1,424,000
Derivative, Fair Value, Net	1,424,000
Cash Flow Hedge Derivative Instrument Liabilities at Fair Value	1,976,000	3,430,000
Cash Flow Hedge Derivative Instrument Liabilities at Fair Value - Gross Liability	1,976,000	3,430,000
Derivative Liability, Fair Value, Gross Liability	0
Derivative Financial Instruments, Assets [Member]
Derivative [Line Items]
Derivative Instrument Not Designated as Hedging Instrument - Gross Liability	(7,576,000)
Derivative Financial Instruments, Liabilities [Member]
Derivative [Line Items]
Derivative Instrument Not Designated as Hedging Instrument - Gross Liability	28,238,000	51,717,000
Nymex Futures Contracts [Member]
Derivative [Line Items]
Derivative Instrument Not Designated as Hedging Instrument - Gross Liability	0	5,563,000
Derivative Instrument Not Designated as Hedging Instrument in Asset Position - Asset	5,471,000
Derivative Instrument not Designated as Hedging Instrument Asset Position - Gross Asset	7,405,000
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	0	5,563,000
Prepayments And Other [Member]
Derivative [Line Items]
Derivative Assets	45,201,000
Other Intangible Assets [Member]
Derivative [Line Items]
Derivative Assets	1,424,000
Forward Contracts [Member]
Derivative [Line Items]
Cash Flow Hedge Derivative Instrument Assets at Fair Value	$ 45,810,000