Supplemental Oil And Natural Gas Disclosures (Unaudited) (Details 5) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Principal Sources of Change in Standardized Measure of Discounted Future Net Cash Flow Relating to Proved Oil and Gas Reserves [Abstract]
Beginning of year	$ 4,917,927,000	$ 2,457,385,000	$ 1,415,498,000
Sales of oil and natural gas produced, net of production costs	(1,597,288,000)	(1,177,322,000)	(498,093,000)
Net changes in sales prices	4,646,086,000	2,062,181,000	1,263,346,000
Previously estimated development costs incurred	354,228,000	193,947,000	98,659,000
Revisions of previous estimates, including revised estimates of development costs, reserves and rates of production	(1,673,283,000)	(285,158,000)	(63,044,000)
Accretion of discount	729,234,000	307,546,000	192,686,000
Acquisition of minerals in place	29,737,000	3,671,439,000	365,771,000
Sales of minerals in place	0	(1,474,443,000)	(419,601,000)
Net change in income taxes	(1,177,114,000)	(1,756,344,000)	(106,717,000)
End of year	7,007,605,000	4,917,927,000	2,457,385,000
Tertiary Recovery [Member]
Principal Sources of Change in Standardized Measure of Discounted Future Net Cash Flow Relating to Proved Oil and Gas Reserves [Abstract]
Extensions and discoveries, less applicable future development and production costs	15,708,000	623,622,000	202,145,000
Non-tertiary
Principal Sources of Change in Standardized Measure of Discounted Future Net Cash Flow Relating to Proved Oil and Gas Reserves [Abstract]
Extensions and discoveries, less applicable future development and production costs	$ 762,370,000	$ 295,074,000	$ 6,735,000