Supplemental Oil And Gas Disclosures (Schedule Of Capitalized Costs And Costs Incurred On Oil And Gas Properties) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Supplemental Oil and Gas Disclosures [Abstract]
Proved properties	$ 3,822,381	$ 3,302,032	$ 2,738,093
Unproved properties	521,659	185,632	175,065
Capitalized costs gross	4,344,040	3,487,664	2,913,158
Accumulated depreciation, depletion, amortization and impairment	(2,216,787)	(1,724,312)	(1,542,352)
Net capitalized costs	2,127,253	1,763,352	1,370,806
Unproved properties acquired	420,467	70,999	75,739
Proved properties acquired	225,669	50,013	50,000
Exploration	46,467	43,836	48,304
Development	390,649	391,862	279,903
Asset retirement obligation	45,097	23,345	9,924
Total costs incurred	$ 1,128,349	$ 580,055	$ 463,870