Derivative Instruments And Hedging Activities (Gain (Loss) Reclassified From Accumulated OCI Into Income) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	$ (84)	$ (6,805)
Oil And Natural Gas Commodity Contracts [Member] | Oil And Gas Revenue [Member]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	109	(6,325)
Interest Rate Contracts [Member] | Net Interest Expense And Other [Member]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	$ (193)	$ (480)