Derivative Instruments And Hedging Activities (Summary Of Balance Sheet Locations And Related Fair Values Of Outstanding Derivative Instruments) (Details) (USD $)	6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 37,989,000
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	1,948,000
Cash Flow Hedge Derivative Instrument Liabilities at Fair Value	0	23,875,000
Derivative Instrument not Designated as Hedging Instrument Asset Position - Gross Asset	15,988,000
Cash Flow Hedge Derivative Instrument Liabilities at Fair Value - Gross Liability	0	41,258,000
Derivative Liability, Fair Value, Gross Liability	(16,070,000)
Interest Rate Cash Flow Hedge Liability at Fair Value	0
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	0
Variable-to-fixed interest rate swap contract, Offsetting Amount	(15,700,000)
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	1,694,000	51,717,000
Derivative Assets	23,867,000
Derivative Liabilities, Current	1,694,000	62,388,000
Derivative Liabilities, Noncurrent		13,204,000
Derivative Liabilities	1,694,000	75,592,000
Commodity Contract [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	35,732,000
Derivative Instrument Not Designated as Hedging Instrument - Gross Liability	0
Cash Flow Hedge Derivative Instrument Assets at Fair Value	0	(17,383,000)
Derivative, Fair Value, Net	21,374,000
Derivative Instrument Not Designated as Hedging Instrument in Asset Position - Asset	1,948,000
Cash Flow Hedge Derivative Instrument Liabilities at Fair Value	0	20,445,000
Derivative Instrument not Designated as Hedging Instrument Asset Position - Gross Asset	15,988,000
Derivative Instrument not Designated as Hedging Instrument Asset Position - Liability	(14,040,000)
Cash Flow Hedge Derivative Instrument Liabilities at Fair Value - Gross Liability	0	37,828,000
Derivative Liability, Fair Value, Gross Liability	(14,358,000)
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	0
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	0
Interest Rate Swap [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	2,257,000
Derivative, Fair Value, Net	545,000
Cash Flow Hedge Derivative Instrument Liabilities at Fair Value	0	3,430,000
Cash Flow Hedge Derivative Instrument Liabilities at Fair Value - Gross Liability	0	3,430,000
Derivative Liability, Fair Value, Gross Liability	(1,712,000)
Derivative Financial Instruments, Assets [Member]
Derivative [Line Items]
Derivative Instrument Not Designated as Hedging Instrument - Gross Liability	(14,040,000)
Derivative Financial Instruments, Liabilities [Member]
Derivative [Line Items]
Derivative Instrument Not Designated as Hedging Instrument - Gross Liability	1,694,000	51,717,000
Nymex Futures Contracts [Member]
Derivative [Line Items]
Derivative Instrument Not Designated as Hedging Instrument - Gross Liability	1,694,000	5,563,000
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	1,694,000	5,563,000
Prepayments And Other [Member]
Derivative [Line Items]
Derivative Assets	39,217,000
Other Intangible Assets [Member]
Derivative [Line Items]
Derivative Assets	2,257,000
Forward Contracts [Member]
Derivative [Line Items]
Cash Flow Hedge Derivative Instrument Assets at Fair Value	21,919,000
Other Long Term Liabilities [Member]
Derivative [Line Items]
Derivative Assets	(17,607,000)
Commodity Contract [Member]
Derivative [Line Items]
Derivative Instrument Not Designated as Hedging Instrument - Gross Liability		46,154,000
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value		$ 46,154,000