Derivative Instruments And Hedging Activities (Gain (Loss) Reclassified From Accumulated OCI Into Income) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	$ 7,903	$ (12,451)	$ 7,819	$ (19,256)
Oil And Natural Gas Commodity Contracts [Member] | Oil And Gas Revenue [Member]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	8,023	(11,860)	8,132	(18,185)
Interest Rate Contracts [Member] | Net Interest Expense And Other [Member]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	$ (120)	$ (591)	$ (313)	$ (1,071)