Derivative Financial Instruments (Derivative Obligations Under Terminated Hedge Arrangements) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Derivative [Line Items]
Amount Of Gain/(Loss) Recognized In AOCI On Effective Portion			$ 12,974
Amount of Gain/(Loss) Reclassified from AOCI into Earnings	32,636	84,877	114,231
Amount of Gain (Loss) Recognized in Earnings on Derivatives	392,752	450,899	(195,557)
Interest Rate Derivatives [Member]
Derivative [Line Items]
Amount Of Gain/(Loss) Recognized In AOCI On Effective Portion			(433)
Interest Rate Derivatives [Member] | Interest Expense [Member]
Derivative [Line Items]
Amount of Gain/(Loss) Reclassified from AOCI into Earnings	(282)	(1,698)	(6,835)
Interest Rate Derivatives [Member] | Derivative Gains (Losses), Net [Member]
Derivative [Line Items]
Amount of Gain/(Loss) Reclassified from AOCI into Earnings		(2,465)
Amount of Gain (Loss) Recognized in Earnings on Derivatives	3,098	36,597	(15,423)
Commodity Price Derivatives [Member]
Derivative [Line Items]
Amount Of Gain/(Loss) Recognized In AOCI On Effective Portion			13,407
Commodity Price Derivatives [Member] | Derivative Gains (Losses), Net [Member]
Derivative [Line Items]
Amount of Gain (Loss) Recognized in Earnings on Derivatives	389,654	414,302	(180,134)
Commodity Price Derivatives [Member] | Oil And Gas revenue [Member]
Derivative [Line Items]
Amount of Gain/(Loss) Reclassified from AOCI into Earnings	$ 32,918	$ 89,040	$ 121,066