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, 2012	Dec. 31, 2011	Dec. 31, 2010
Supplemental Oil and Gas Disclosures [Abstract]
Future net cash flows relating to proved oil and gas reserves future cash inflows	$ 4,522,351	$ 4,583,629	$ 3,745,046
Future production costs	(1,405,773)	(1,277,856)	(1,054,630)
Future development costs	(431,673)	(340,992)	(303,152)
Future income tax expenses	(762,519)	(952,736)	(799,260)
Future net cash flows	1,922,386	2,012,045	1,588,004
10% annual discount for estimated timing of cash flows	842,430	924,136	732,918
Standardized measure of discounted future net cash flows relating to proved oil, NGLs and natural gas reserves	$ 1,079,956	$ 1,087,909	$ 855,086
Percentage of annual discount for estimated timing of cash flows	10.00%	10.00%	10.00%