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, 2012	Dec. 31, 2011	Dec. 31, 2010
Reserve Quantities [Line Items]
Sales and transfers of oil and natural gas produced, net of production costs	$ (425,626)	$ (389,339)	$ (301,086)
Net changes in prices and production costs	(321,099)	115,852	379,097
Revisions in quantity estimates and changes in production timing	(148,648)	(38,336)	(67,116)
Extensions, discoveries and improved recovery, less related costs	432,058	401,134	340,771
Changes in estimated future development costs	51,587	37,742	15,974
Previously estimated cost incurred during the period	104,377	45,327	45,327
Purchases of minerals in place	283,774	58,567	42,280
Sales of minerals in place	(112,359)	(29)	(120)
Accretion of discount	157,842	128,492	77,536
Net change in income taxes	94,678	(60,675)	(200,815)
Other-net	(124,537)	(65,912)	(23,097)
Net change	(7,953)	232,823	308,751
Beginning of year	1,087,909	855,086	546,335
End of year	$ 1,079,956	$ 1,087,909	$ 855,086