Derivative Instruments And Hedging Activities (Impact Of Derivative Instruments On Accumulated Comprehensive Income (Loss)) (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) Recognized in OCI on Derivatives (Effective Portion)	$ 12,680	$ 20,970	$ (1,122)	$ 10,403
Oil And Natural Gas Commodity Contracts [Member]
Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)	12,759	20,720	(796)	9,942
Interest Rate Contracts [Member]
Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)	$ (79)	$ 250	$ (326)	$ 461