Supplemental Oil And Gas Disclosures (Schedule Of Principal Sources Of Changes In Standardized Measure Of Discounted Future Net Cash Flows) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Reserve Quantities [Line Items]
Sales and transfers of oil and natural gas produced, net of production costs	$ (389,339)	$ (301,086)	$ (277,358)
Net changes in prices and production costs	115,852	379,097	(145,839)
Revisions in quantity estimates and changes in production timing	(38,336)	(67,116)	(54,327)
Extensions, discoveries and improved recovery, less related costs	401,134	340,771	136,695
Changes in estimated future development costs	37,742	15,974	100,304
Previously estimated cost incurred during the period	45,327	45,327	16,301
Purchases of minerals in place	58,567	42,280	1,288
Sales of minerals in place	(29)	(120)	0
Accretion of discount	128,492	77,536	89,256
Net change in income taxes	(60,675)	(200,815)	39,062
Other-net	(65,912)	(23,097)	16,479
Net change	232,823	308,751	(78,139)
Beginning of year	855,086	546,335	624,474
End of year	$ 1,087,909	$ 855,086	$ 546,335
Oil [Member]
Reserve Quantities [Line Items]
Average prices of oil and gas	$ 96.19
Natural Gas Liquids [Member]
Reserve Quantities [Line Items]
Average prices of oil and gas	$ 61.78
Natural Gas [Member]
Reserve Quantities [Line Items]
Average prices of oil and gas	$ 4.12