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, 2016	Dec. 31, 2015	Dec. 31, 2014
Reserve Quantities [Line Items]
Sales and transfers of oil and natural gas produced, net of production costs	$ (173,920)	$ (218,115)	$ (558,252)
Net changes in prices and production costs	(94,026)	(1,356,333)	(33,259)
Revisions in quantity estimates and changes in production timing	(51,979)	(213,945)	(135,125)
Extensions, discoveries, and improved recovery, less related costs	84,738	95,671	635,752
Changes in estimated future development costs	70,976	227,857	96,339
Previously estimated cost incurred during the period	16,602	59,117	164,430
Purchases of minerals in place	2,652	0	8,395
Sales of minerals in place	(17,248)	(3,338)	(19,135)
Accretion of discount	69,069	209,979	179,190
Net change in income taxes	44,241	562,838	(98,119)
Other-net	(22,381)	(209,989)	(30,448)
Net change	(71,276)	(846,258)	209,768
Beginning of year	589,486	1,435,744	1,225,976
End of year	$ 518,210	$ 589,486	$ 1,435,744