Derivative Instruments And Hedging Activities (Derivatives Designated As Hedging Instruments) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Asset derivatives designated as hedging instruments	$ 20,322	$ 22,708
Liability derivatives designated as hedging instruments	23,985	2,799
Other Current Assets [Member] | Oil Contract [Member]
Asset derivatives designated as hedging instruments	931	8,567
Other Current Assets [Member] | Natural Gas Contracts [Member]
Asset derivatives designated as hedging instruments	16,744	12,957
Other Assets, Net [Member] | Natural Gas Contracts [Member]
Asset derivatives designated as hedging instruments	2,564	857
Other Assets, Net [Member] | Interest Rate Swaps [Member]
Asset derivatives designated as hedging instruments	83	327
Other Liabilities [Member] | Oil Contract [Member]
Liability derivatives designated as hedging instruments	8,831	1,711
Accrued Liabilities [Member] | Oil Contract [Member]
Liability derivatives designated as hedging instruments	14,816	886
Accrued Liabilities [Member] | Interest Rate Swaps [Member]
Liability derivatives designated as hedging instruments	$ 338	$ 202