Derivative Instruments And Hedging Activities (Summary Of Balance Sheet Locations And Related Fair Values Of Outstanding Derivative Instruments) (Details) (USD $)	9 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Derivative [Line Items]
Commodity price swap contracts, Fair Value		$ 173,784,000
Interest Rate Derivatives, at Fair Value, Net	90,709,000	520,000
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	4,126,000
Interest Rate Cash Flow Hedge Liability at Fair Value	3,764,000	520,000
Cash Flow Hedge Derivative Instrument Liabilities at Fair Value	22,018,000
Derivative Financial Instruments, Liabilities, Fair Value Disclosure	86,945,000
Variable-to-fixed interest rate swap contract, Offsetting Amount	(68,700,000)
Derivatives not designated as hedge liability, Fair Value	20,986,000	1,870,000
Derivatives not designated as hedge liability, Offsetting Amount	13,516,000	1,252,000
Other Derivatives Not Designated as Hedging Instruments at Fair Value, Net	$ 25,112,000