Derivative Instruments And Hedging Activities (Impact Of Derivative Instruments On Accumulated Comprehensive Income (Loss)) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)	$ (13,802)	$ (10,567)
Oil And Natural Gas Commodity Contracts [Member]
Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)	(13,555)	(10,778)
Interest Rate Contracts [Member]
Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)	$ (247)	$ 211