Supplemental Oil And Gas Disclosures (Results Of Operations For Producing Activities) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Supplemental Oil and Gas Disclosures [Abstract]
Revenues	$ 557,003	$ 505,450	$ 392,229
Production costs	(131,389)	(115,400)	(91,143)
Depreciation, depletion, amortization and impairment	(492,475)	(181,960)	(117,793)
Results of operations, income before income taxes	(66,861)	208,090	183,293
Income tax (expense) benefit	27,533	(80,323)	(70,110)
Results of operations for producing activities (excluding corporate overhead and financing costs)	$ (39,328)	$ 127,767	$ 113,183