Derivative Instruments And Hedging Activities (Summary Of Balance Sheet Locations And Related Fair Values Of Outstanding Derivative Instruments) (Details) (USD $)	6 Months Ended	12 Months Ended
	Jun. 30, 2012	Dec. 31, 2011
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 119,461,000
Derivative Assets, Current	75,840,000
Commodity price swap contracts, Fair Value	119,461,000	173,784,000
Interest Rate Derivatives, at Fair Value, Net	78,222,000	520,000
Interest Rate Cash Flow Hedge Liability at Fair Value	2,382,000	520,000
Variable-to-fixed interest rate swap contract, Offsetting Amount	41,200,000
Derivatives not designated as hedge liability, Fair Value	6,372,000	1,870,000
Derivatives not designated as hedge liability, Offsetting Amount	$ 16,043,000	$ 1,252,000