Derivative Financial Instruments (Derivative Obligations Under Terminated Hedge Arrangements) (Details) (USD $) In Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Amount of Gain/(Loss) Reclassified from AOCI into Earnings	$ 8,139	$ 20,697	$ 16,195	$ 41,623
Amount of Gain (Loss) Recognized in Earnings on Derivatives	229,478	179,051	(14,954)	445,669
Interest Rate Derivatives [Member] | Interest Expense [Member]
Amount of Gain/(Loss) Reclassified from AOCI into Earnings	(69)	(312)	(137)	(1,370)
Interest Rate Derivatives [Member] | Derivative Gains (Losses), Net [Member]
Amount of Gain/(Loss) Reclassified from AOCI into Earnings		(1,523)		(2,665)
Amount of Gain (Loss) Recognized in Earnings on Derivatives	14,575	26,517	12,423	37,916
Commodity Price Derivatives [Member] | Derivative Gains (Losses), Net [Member]
Amount of Gain (Loss) Recognized in Earnings on Derivatives	214,903	152,534	(27,377)	407,753
Commodity Price Derivatives [Member] | Oil And Gas revenue [Member]
Amount of Gain/(Loss) Reclassified from AOCI into Earnings	$ 8,208	$ 22,532	$ 16,332	$ 45,658