Derivative Instruments And Hedging Activities (Derivatives Designated As Hedging Instruments) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Asset derivatives designated as hedging instruments	$ 32,672	$ 22,708
Liability derivatives designated as hedging instruments	6,759	2,799
Other Current Assets [Member] | Oil Contract [Member]
Asset derivatives designated as hedging instruments	16,033	8,567
Other Current Assets [Member] | Natural Gas Contracts [Member]
Asset derivatives designated as hedging instruments	9,663	12,957
Other Assets, Net [Member] | Oil Contract [Member]
Asset derivatives designated as hedging instruments	5,737
Other Assets, Net [Member] | Natural Gas Contracts [Member]
Asset derivatives designated as hedging instruments	1,239	857
Other Assets, Net [Member] | Interest Rate Swaps [Member]
Asset derivatives designated as hedging instruments		327
Other Liabilities [Member] | Oil Contract [Member]
Liability derivatives designated as hedging instruments	1,059	1,711
Other Liabilities [Member] | Interest Rate Swaps [Member]
Liability derivatives designated as hedging instruments	59
Accrued Liabilities [Member] | Oil Contract [Member]
Liability derivatives designated as hedging instruments	5,324	886
Accrued Liabilities [Member] | Interest Rate Swaps [Member]
Liability derivatives designated as hedging instruments	$ 317	$ 202