Supplemental Oil And Gas Disclosures (Standardized Measure Of Discounted Future Cash Flows Relating To Proved Reserves Disclosure) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Supplemental Oil And Gas Disclosures [Abstract]
Future cash flows	$ 4,583,629	$ 3,745,046	$ 2,403,892
Future production costs	(1,277,856)	(1,054,630)	(777,725)
Future development costs	(340,992)	(303,152)	(195,486)
Future income tax expenses	(952,736)	(799,260)	(433,366)
Future net cash flows	2,012,045	1,588,004	997,315
10% annual discount for estimated timing of cash flows	(924,136)	(732,918)	(450,980)
Standardized measure of discounted future net cash flows relating to proved oil, NGLs and natural gas reserves	$ 1,087,909	$ 855,086	$ 546,335
Percentage of annual discount for estimated timing of cash flows	10.00%	10.00%	10.00%