Derivative Instruments And Hedging Activities (Gain (Loss) Reclassified From Accumulated OCI Into Income) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Derivatives, Fair Value [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income	$ (23,669)	$ 23,726	$ 15,876
Oil And Natural Gas Commodity Contracts [Member] | Gain On Oil And Gas Derivative Contracts [Member]
Derivatives, Fair Value [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income	(21,659)	25,575	16,972
Interest Rate Swaps [Member] | Net Interest Expense [Member]
Derivatives, Fair Value [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income	$ (2,010)	$ (1,849)	$ (1,096)