Derivative Instruments And Hedging Activities (Gain (Loss) Reclassified From Accumulated OCI Into Income) (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) Reclassified from Accumulated OCI into Income (Effective Portion)	$ 293	$ (1,809)	$ 8,112	$ (20,986)
Oil And Natural Gas Commodity Contracts [Member] | Oil And Gas Revenue [Member]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	414	(1,287)	8,546	(19,473)
Interest Rate Swaps [Member] | Net Interest Expense And Other [Member]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	$ (121)	$ (522)	$ (434)	$ (1,513)