Exploratory Costs (Schedule Of Capitalized Exploratory Well And Project Activity) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Exploratory Cost Disclosure [Abstract]
Beginning capitalized exploratory costs	$ 212,670
Additions to exploratory costs pending the determination of proved reserves	351,575
Reclassification due to determination of proved reserves	(262,754)
Exploratory well costs charged to exploration expense	(7,734)
Ending capitalized exploratory costs	293,757
Capitalized exploratory costs that have been suspended, One year or less	174,841	190,678
Capitalized Exploratory Well Costs that Have Been Capitalized for Period Greater than One Year	$ 118,916	$ 21,992
Number of projects with exploratory costs that have been suspended for a period greater than one year	2	1