Derivative Financial Instruments (Schedule Of Derivative Obligations Under Terminated Hedge Arrangements) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Derivative [Line Items]
Amount of Gain/(Loss) Reclassified from AOCI into Earnings	$ (2,508)	$ 8,056
Interest Rate Derivatives [Member] | Interest Expense [Member]
Derivative [Line Items]
Amount of Gain/(Loss) Reclassified from AOCI into Earnings	(1,698)	(68)
Interest Rate Derivatives [Member] | Derivative Gains, Net [Member]
Derivative [Line Items]
Amount of Gain (Loss) Recognized in Earnings on Derivatives	3,620	(2,152)
Commodity Price Derivatives [Member] | Derivative Gains, Net [Member]
Derivative [Line Items]
Amount of Gain (Loss) Recognized in Earnings on Derivatives	88,130	(242,280)
Commodity Price Derivatives [Member] | Oil And Gas revenue [Member]
Derivative [Line Items]
Amount of Gain/(Loss) Reclassified from AOCI into Earnings	$ (810)	$ 8,124