Supplemental Oil And Gas Disclosures (Schedule Of Principal Sources Of Changes In Standardized Measure Of Discounted Future Net Cash Flows) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Reserve Quantities [Line Items]
Sales and transfers of oil and natural gas produced, net of production costs	$ (218,115)	$ (558,252)	$ (470,970)
Net changes in prices and production costs	(1,356,333)	(33,259)	188,826
Revisions in quantity estimates and changes in production timing	(213,945)	(135,125)	(10,650)
Extensions, discoveries, and improved recovery, less related costs	95,671	635,752	426,377
Changes in estimated future development costs	227,857	96,339	26,629
Previously estimated cost incurred during the period	59,117	164,430	96,457
Purchases of minerals in place	0	8,395	9
Sales of minerals in place	(3,338)	(19,135)	(43,435)
Accretion of discount	209,979	179,190	147,579
Net change in income taxes	562,838	(98,119)	(170,091)
Other-net	(209,989)	(30,448)	(44,711)
Net change	(846,258)	209,768	146,020
Beginning of year	1,435,744	1,225,976	1,079,956
End of year	$ 589,486	$ 1,435,744	$ 1,225,976