Risk Management Activities (Details) (USD $)	3 Months Ended		6 Months Ended											6 Months Ended		12 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011	Jun. 30, 2012 Crude Oil and Natural Gas Derivative Contracts [Member] Assets From Price Risk Management Activities [Member]	Dec. 31, 2011 Crude Oil and Natural Gas Derivative Contracts [Member] Assets From Price Risk Management Activities [Member]	Jun. 30, 2012 Crude Oil and Natural Gas Derivative Contracts [Member] Other Assets [Member]	Dec. 31, 2011 Crude Oil and Natural Gas Derivative Contracts [Member] Other Assets [Member]	Jun. 30, 2012 Interest Rate Swap [Member] Other Liabilities [Member]	Dec. 31, 2011 Interest Rate Swap [Member] Other Liabilities [Member]	Jun. 30, 2012 Foreign Currency Swap [Member] Other Liabilities [Member]	Dec. 31, 2011 Foreign Currency Swap [Member] Other Liabilities [Member]	Jun. 30, 2012 Crude Oil Derivative Contracts January - February [Member]	Jun. 30, 2012 Natural Gas Derivative Contracts January - July [Member]	Dec. 31, 2013 Natural Gas Derivative Contracts Year Two January - December [Member]	Dec. 31, 2014 Natural Gas Derivative Contracts Year Three January - December [Member]	Jun. 30, 2012 Natural Gas Derivative Contracts - August - December [Member]	Jun. 30, 2012 Crude Oil Derivative Contracts January - June [Member]	Jun. 30, 2012 Crude Oil Derivative Contracts March - June [Member]	Jun. 30, 2012 Crude Oil Derivative Contracts July - August [Member]	Jun. 30, 2012 Crude Oil Derivative Contracts September - December [Member]	Jun. 30, 2012 Crude Oil Derivative Contracts September - February [Member]
Derivative [Line Items]
Natural Gas Derivative, Counterparty															525,000	150,000	150,000	525,000
Volume (Bbld)														34,000						52,000	50,000	32,000
Volumes (MMBtud) - Derivative Option Contracts																150,000	150,000	425,000
Average Price ($/MMBtu) - Derivative Option Contracts																4.79	4.79	5.44
Derivative Weighted Average Price Crude Oil ($/Bbl)														104.95						105.80	106.90	106.61
Derivative Weighted Average Price Natural Gas ($/MMBtu)															5.44	4.79	4.79	5.44
Volumes (Bbld) - Derivative Option Contracts																			15,000				18,000
Average Price ($/Bbl) - Derivative Option Contracts																			110.03				107.42
Proceeds from financial derivative contracts settled subsequent to end of period			$ 36,600,000
Derivatives, Fair Value [Line Items]
Derivatives Assets, Current	421,135,000		421,135,000		450,730,000	410,000,000	451,000,000
Other Assets								54,000,000	35,000,000
Other Liabilities										4,000,000	3,000,000	51,000,000	52,000,000
Foreign Currency Exchange Rate Derivative [Abstract]
Debt Instrument Issuance Face Value	150,000,000		150,000,000
After-Tax Net Impact Other Comprehensive Income Increase (Decrease) From The Foreign Currency Swap	1,000,000	1,000,000	1,000,000	(100,000)
Interest Rate Cash Flow Hedges [Abstract]
Interest Rate Swap, Notional Amount	350,000,000		350,000,000
After-Tax Net Impact From Interest Rate Swap	100,000	(4,000,000)	(200,000)	(3,000,000)
Derivative Collateral [Abstract]
Collateral Held on Derivative	$ 100,000,000		$ 100,000,000		$ 67,000,000