Derivative Financial Instruments (Derivative Obligations Under Terminated Hedge Arrangements) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Derivative [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment on Derivatives Included in Net Income, before Tax	$ 0	$ (4,855)	$ 32,636
Amount of Gain (Loss) Recognized in Earnings on Derivatives	4,010	330,251	392,752
Interest Rate Derivatives [Member]
Derivative [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment on Derivatives Included in Net Income, before Tax		(1,700)	(282)
Interest Rate Derivatives [Member] | Interest Expense [Member]
Derivative [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment on Derivatives Included in Net Income, before Tax	0	(1,699)	(282)
Interest Rate Derivatives [Member] | Derivative Gains (Losses), Net [Member]
Derivative [Line Items]
Amount of Gain (Loss) Recognized in Earnings on Derivatives	9,803	(22,428)	3,098
Commodity Price Derivatives [Member] | Oil And Gas revenue [Member]
Derivative [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment on Derivatives Included in Net Income, before Tax	0	(3,156)	32,918
Commodity Price Derivatives [Member] | Derivative Gains (Losses), Net [Member]
Derivative [Line Items]
Amount of Gain (Loss) Recognized in Earnings on Derivatives	$ (5,793)	$ 352,679	$ 389,654