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, 2013	Dec. 31, 2012	Dec. 31, 2011
Supplemental Oil and Gas Disclosures [Abstract]
Proved properties	$ 4,235,712	$ 3,822,381	$ 3,302,032
Unproved properties not being amortized	545,588	521,659	185,632
Capitalized costs gross	4,781,300	4,344,040	3,487,664
Accumulated depreciation, depletion, amortization and impairment	(2,439,458)	(2,216,787)	(1,724,312)
Net capitalized costs	2,341,842	2,127,253	1,763,352
Unproved properties acquired	76,304	420,467	70,999
Proved properties acquired	0	225,669	50,013
Exploration	33,373	46,467	43,836
Development	424,314	390,649	391,862
Asset retirement obligation	(17,951)	45,097	23,345
Total costs incurred	$ 516,040	$ 1,128,349	$ 580,055