Derivative Financial Instruments (Schedule Of Derivative Instruments) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Derivative [Line Items]
Derivative Assets, Current	$ 151,431	$ 279,119
Derivative Assets, Noncurrent	95,121	55,257
Derivative Asset, Fair Value, Net	246,552
Derivative Liabilities, Current	20,413	13,416
Derivative Liabilities, Noncurrent	13,372	12,307
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Net	246,552	334,376
Derivative Liability, Fair Value, Net	33,785	25,723
Not Designated as Hedging Instrument [Member] | Commodity Price Derivatives [Member] | Derivatives - Current [Member]
Derivative [Line Items]
Total derivatives, Asset, Gross	160,149	286,805
Total derivatives, Liability. Gross	29,131	21,102
Derivative Assets and Liabilities Offset In Balance Sheet	(8,718)	(7,686)
Derivative Assets, Current	151,431	279,119
Derivative Liabilities, Current	20,413	13,416
Not Designated as Hedging Instrument [Member] | Commodity Price Derivatives [Member] | Derivatives - Noncurrent [Member]
Derivative [Line Items]
Total derivatives, Asset, Gross	100,090	61,618
Total derivatives, Liability. Gross	12,557	8,944
Derivative Assets and Liabilities Offset In Balance Sheet	(4,969)	(6,361)
Derivative Assets, Noncurrent	95,121	55,257
Derivative Liabilities, Noncurrent	7,588	2,583
Not Designated as Hedging Instrument [Member] | Interest Rate Derivatives [Member] | Derivatives - Noncurrent [Member]
Derivative [Line Items]
Total derivatives, Liability. Gross	5,784	9,724
Derivative Assets and Liabilities Offset In Balance Sheet	0	0
Derivative Liabilities, Noncurrent	$ 5,784	$ 9,724