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, 2011	Dec. 31, 2010	Dec. 31, 2009
Supplemental Oil And Gas Disclosures [Abstract]
Proved properties	$ 3,302,032	$ 2,738,093	$ 2,309,193
Unproved properties	185,632	175,065	140,129
Capitalized costs gross	3,487,664	2,913,158	2,449,322
Accumulated depreciation, depletion, amortization and impairment	(1,724,312)	(1,542,352)	(1,424,559)
Net capitalized costs	1,763,352	1,370,806	1,024,763
Unproved properties acquired	70,999	75,739	37,137
Proved properties acquired	50,013	50,000	3,722
Exploration	43,836	48,304	30,547
Development	391,862	279,903	154,579
Asset retirement obligation	23,345	9,924	4,565
Total costs incurred	$ 580,055	$ 463,870	$ 230,550