Derivative Instruments And Hedging Activities (Impact Of Derivative Instruments On Accumulated Comprehensive Income (Loss)) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)	$ (12,941)	$ 30,043	$ (7,699)
Oil And Natural Gas Commodity Contracts [Member]
Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)	(12,860)	28,749	(6,486)
Interest Rate Swaps [Member]
Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)	$ (81)	$ 1,294	$ (1,213)