Derivative Instruments And Hedging Activities (Impact Of Derivative Instruments On Accumulated Comprehensive Income (Loss)) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)	$ (20,036)	$ 33,888	$ (21,158)	$ 44,291
Oil And Natural Gas Commodity Contracts [Member]
Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)	(19,868)	33,432	(20,664)	43,373
Interest Rate Swaps [Member]
Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)	$ (168)	$ 456	$ (494)	$ 918