Supplemental Oil And Gas Disclosures (Schedule Of Principal Sources Of Changes In Standardized Measure Of Discounted Future Net Cash Flows) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reserve Quantities [Line Items]
Sales and transfers of oil and natural gas produced, net of production costs	$ (558,252)	$ (470,970)	$ (425,626)
Net changes in prices and production costs	(33,259)	188,826	(321,099)
Revisions in quantity estimates and changes in production timing	(135,125)	(10,650)	(148,648)
Extensions, discoveries, and improved recovery, less related costs	635,752	426,377	432,058
Changes in estimated future development costs	96,339	26,629	51,587
Previously estimated cost incurred during the period	164,430	96,457	104,377
Purchases of minerals in place	8,395	9	283,774
Sales of minerals in place	(19,135)	(43,435)	(112,359)
Accretion of discount	179,190	147,579	157,842
Net change in income taxes	(98,119)	(170,091)	94,678
Other-net	(30,448)	(44,711)	(124,537)
Net change	209,768	146,020	(7,953)
Beginning of year	1,225,976	1,079,956	1,087,909
End of year	$ 1,435,744	$ 1,225,976	$ 1,079,956