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	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Derivatives, Fair Value [Line Items]
Cash Flow Hedge Derivative Instrument Liabilities at Fair Value	$ 17,383
Commodity price swap contracts, Fair Value		173,784
Interest Rate Derivatives, at Fair Value, Net	41,258	520
Derivatives not designated as hedge liability, Fair Value		1,870
Derivatives not designated as hedge liability, Offsetting Amount	51,717
Accrued liabilities
Derivatives, Fair Value [Line Items]
Derivative Financial Instruments, Liabilities, Fair Value Disclosure	28,054
Derivatives not designated as hedge liability, Offsetting Amount	51,717	1,252
Other long-term liabilities
Derivatives, Fair Value [Line Items]
Derivative Financial Instruments, Liabilities, Fair Value Disclosure	9,774
Interest Rate Cash Flow Hedge Liability at Fair Value	$ 3,430	$ 520