Oil and Natural Gas Capitalized Costs (Details) (USD $) In Thousands	Sep. 30, 2011	Dec. 31, 2010
Proved properties:
Leasehold acquisition	$ 5,483,984	$ 4,695,704
Development	1,262,251	840,175
Unproved properties	194,543	128,624
Oil and natural gas properties (successful efforts method)	6,940,778	5,664,503
Less accumulated depletion and amortization	(939,264)	(719,035)
Oil and natural gas properties, successful efforts method, net	$ 6,001,514	$ 4,945,468

Oil and Gas properties with unproved reserves under the successful effort method.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

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+ Details