Derivative Instruments And Hedging Activities (Summary Of Balance Sheet Locations And Related Fair Values Of Outstanding Derivative Instruments) (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Loss	$ 0
Cash Flow Hedge Derivative Instrument Assets at Fair Value	(27,144,000)	(17,383,000)
Cash Flow Hedge Derivative Instrument Liabilities at Fair Value	354,000	23,875,000
Derivative Instrument not Designated as Hedging Instrument Asset Position - Gross Asset	12,493,000
Cash Flow Hedge Derivative Instrument Liabilities at Fair Value - Gross Liability	27,498,000	41,258,000
Interest Rate Cash Flow Hedge Liability at Fair Value	0
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	10,651,000
Variable-to-fixed interest rate swap contract, Offsetting Amount	4,300,000
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	13,844,000	51,717,000
Derivative Assets	12,119,000
Derivative Liabilities, Current	562,000	62,388,000
Derivative Liabilities, Noncurrent	13,636,000	13,204,000
Derivative Liabilities	14,198,000	75,592,000
Derivative Financial Instruments, Assets [Member]
Derivative [Line Items]
Derivative Instrument Not Designated as Hedging Instrument - Gross Liability	(1,842,000)
Derivative Assets	12,119,000
Nymex Futures Contracts [Member]
Derivative [Line Items]
Derivative Instrument Not Designated as Hedging Instrument - Gross Liability	5,837,000	5,563,000
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	5,837,000	5,563,000
Forward Contracts [Member]
Derivative [Line Items]
Cash Flow Hedge Derivative Instrument Assets at Fair Value	1,468,000
Interest Rate Swap [Member]
Derivative [Line Items]
Cash Flow Hedge Derivative Instrument Liabilities at Fair Value	2,868,000	3,430,000
Cash Flow Hedge Derivative Instrument Liabilities at Fair Value - Gross Liability	2,868,000	3,430,000
Commodity Contract [Member]
Derivative [Line Items]
Derivative Instrument Not Designated as Hedging Instrument - Gross Liability	12,178,000
Cash Flow Hedge Derivative Instrument Assets at Fair Value	(27,144,000)	(17,383,000)
Derivative Instrument Not Designated as Hedging Instrument in Asset Position - Asset	10,651,000
Cash Flow Hedge Derivative Instrument Liabilities at Fair Value	(2,514,000)	20,445,000
Derivative Instrument not Designated as Hedging Instrument Asset Position - Gross Asset	12,493,000
Derivative Instrument not Designated as Hedging Instrument Asset Position - Liability	(1,842,000)
Cash Flow Hedge Derivative Instrument Liabilities at Fair Value - Gross Liability	24,630,000	37,828,000
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	(4,171,000)
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	8,007,000
Derivative Financial Instruments, Liabilities [Member]
Derivative [Line Items]
Derivative Instrument Not Designated as Hedging Instrument - Gross Liability	18,015,000	51,717,000
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