Derivatives And Fair Value Measurements (Carrying Value Of Derivatives) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Derivatives, Fair Value [Line Items]
Settlements in production revenue	$ (14,755)	$ (28,589)
Cash Flow Derivatives [Member]
Derivatives, Fair Value [Line Items]
Derivative fair value at beginning of period		342,799
Ineffectiveness reported in net derivative gains (losses)		(5,241)
Unrealized gains (losses) reported in OCI		99,894
Derecognition of hedges		(180,732)
Derivative fair value at end of period		211,163
Production Revenue [Member] | Cash Flow Derivatives [Member]
Derivatives, Fair Value [Line Items]
Settlements in production revenue		(41,737)
Derivative gains (losses) [Member] | Cash Flow Derivatives [Member]
Derivatives, Fair Value [Line Items]
Settlements in net derivative (gains) losses		$ (3,820)