Supplemental Oil And Gas Disclosures (Schedule Of Capitalized Costs And Costs Incurred On Oil And Gas Properties) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Capitalized costs:
Proved properties	$ 5,401,618	$ 4,990,753	$ 4,235,712
Unproved properties not being amortized	337,099	485,568	545,588
Capitalized costs gross	5,738,717	5,476,321	4,781,300
Accumulated depreciation, depletion, amortization, and impairment	(4,631,404)	(2,786,678)	(2,439,458)
Net capitalized costs	1,107,313	2,689,643	2,341,842
Costs incurred:
Unproved properties acquired	41,777	76,041	76,304
Proved properties acquired	179	5,723	0
Exploration	19,222	68,811	33,373
Development	208,845	615,252	424,314
Asset retirement obligation	(5,693)	(37,687)	(17,951)
Total costs incurred	$ 264,330	$ 728,140	$ 516,040