Risk Management Activities (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Derivatives, Fair Value [Line Items]
Derivatives Assets, Current	$ 32,711,000		$ 166,135,000
Derivative Liabilities, Current	14,108,000		7,617,000
Foreign Currency Exchange Rate Derivative [Abstract]
After-Tax Net Impact Other Comprehensive Income Increase (Decrease) From The Foreign Currency Swap	1,700,000	1,500,000
Interest Rate Derivative [Abstract]
Interest Rate Swap, Notional Amount	350,000,000
After-Tax Net Impact Other Comprehensive Income Increase (Decrease) From Interest Rate Swap	500,000	(400,000)
Derivative Collateral [Abstract]
Collateral Held on Derivative	0		6,000,000
Crude Oil and Natural Gas Derivative Contracts [Member] | Assets From Price Risk Management Activities [Member]
Derivatives, Fair Value [Line Items]
Derivatives Assets, Current	33,000,000		166,000,000
Derivative Assets, Current, Gross	72,000,000		257,000,000
Derivative Liabilities, Current, Gross	39,000,000		91,000,000
Crude Oil and Natural Gas Derivative Contracts [Member] | Liabilities From Price Risk Management Activities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liabilities, Current	14,000,000		8,000,000
Derivative Assets, Current, Gross	14,000,000		9,000,000
Derivative Liabilities, Current, Gross	28,000,000		17,000,000
Crude Oil and Natural Gas Derivative Contracts [Member] | Other Liabilities [Member]
Derivatives, Fair Value [Line Items]
Other Liabilities	45,000,000		13,000,000
Derivative Assets, Noncurrent, Gross	11,000,000
Derivative Liabilities, Noncurrent, Gross	56,000,000		13,000,000
Foreign Currency Swap [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liabilities, Current	49,000,000		0
Foreign Currency Swap [Member] | Other Liabilities [Member]
Derivatives, Fair Value [Line Items]
Other Liabilities	0		55,000,000
Interest Rate Swap [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liabilities, Current	3,000,000		0
Interest Rate Swap [Member] | Other Liabilities [Member]
Derivatives, Fair Value [Line Items]
Other Liabilities	$ 0		$ 4,000,000
Crude Oil Derivative Contracts January (closed) [Member]
Derivative [Line Items]
Volume (Bbld)	101,000
Derivative Weighted Average Price Crude Oil ($/Bbl)	99.29
Crude Oil Derivative Contracts February - March (closed) [Member]
Derivative [Line Items]
Volume (Bbld)	109,000
Derivative Weighted Average Price Crude Oil ($/Bbl)	99.17
Crude Oil Derivative Contracts April [Member]
Derivative [Line Items]
Volume (Bbld)	109,000
Derivative Weighted Average Price Crude Oil ($/Bbl)	99.17
Crude Oil Derivative Contracts May - June [Member]
Derivative [Line Items]
Volume (Bbld)	101,000
Derivative Weighted Average Price Crude Oil ($/Bbl)	99.29
Crude Oil Derivative Contracts July - December [Member]
Derivative [Line Items]
Volume (Bbld)	93,000
Derivative Weighted Average Price Crude Oil ($/Bbl)	98.44
Volumes (Bbld) - Derivative Option Contracts	62,000
Average Price ($/Bbl) - Derivative Option Contracts	100.24
Crude Oil Derivative Contracts May - July [Member]
Derivative [Line Items]
Volumes (Bbld) - Derivative Option Contracts	8,000
Average Price ($/Bbl) - Derivative Option Contracts	97.66
Crude Oil Derivative Contracts Year Two January - December [Member]
Derivative [Line Items]
Volume (Bbld)	40,000
Derivative Weighted Average Price Crude Oil ($/Bbl)	95.77
Crude Oil Derivative Contracts Year Two January - June [Member]
Derivative [Line Items]
Volumes (Bbld) - Derivative Option Contracts	54,000
Average Price ($/Bbl) - Derivative Option Contracts	98.91
Crude Oil Derivative Contracts Year Two July - December [Member]
Derivative [Line Items]
Volumes (Bbld) - Derivative Option Contracts	40,000
Average Price ($/Bbl) - Derivative Option Contracts	95.77
Natural Gas Derivative Contracts January - April (closed) [Member]
Derivative [Line Items]
Volume (MMBtud)	150,000
Derivative Weighted Average Price Natural Gas ($/MMBtu)	4.79
Natural Gas Derivative Contracts May - December [Member]
Derivative [Line Items]
Volume (MMBtud)	150,000
Derivative Weighted Average Price Natural Gas ($/MMBtu)	4.79
Volumes (MMBtud) - Derivative Option Contracts	150,000
Average Price ($/MMBtu) - Derivative Option Contracts	4.79
Natural Gas Derivative Contracts Year Two January - December [Member]
Derivative [Line Items]
Volume (MMBtud)	100,000
Derivative Weighted Average Price Natural Gas ($/MMBtu)	4.48
Volumes (MMBtud) - Derivative Option Contracts	250,000
Average Price ($/MMBtu) - Derivative Option Contracts	4.66