Supplemental Oil and Natural Gas Disclosures (Unaudited) (Details 4) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves, Standardized Measure [Abstract]
Future cash inflows	$ 38,165,122,000	$ 26,698,819,000	$ 11,579,159,000
Future production costs	(12,570,015,000)	(9,702,896,000)	(5,034,393,000)
Future development costs	(3,026,898,000)	(1,912,457,000)	(836,455,000)
Future income taxes	(7,379,972,000)	(4,700,023,000)	(1,257,844,000)
Future net cash flows	15,188,237,000	10,383,443,000	4,450,467,000
10% annual discount for estimated timing of cash flows	(8,180,632,000)	(5,465,516,000)	(1,993,082,000)
Standardized measure of discounted future net cash flows	$ 7,007,605,000	$ 4,917,927,000	$ 2,457,385,000