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Supplemental Oil And Gas Reserve Information - Unaudited (Changes In The Standardized Measure Of Discounted Future Net Cash Flows Applicable To Proved Oil And Natural Gas Reserves) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Supplemental Oil And Gas Reserve Information [Line Items]
January 1,	$ 485,735	$ 133,530	$ 17,730
Net changes in prices and production costs	299,108	126,089	11,423
Net changes in future development costs	(38,244)	(9,767)	1,998
Sales of oil and natural gas, net	(262,485)	(100,577)	(25,254)
Purchases of reserves in place	2,679	26,919	36,809
Sales of reserves in place	(2,499)	(1,720)	(108)
Revisions of previous quantity estimates	(5,058)	55,149	7,700
Previously estimated development costs incurred	146,847	32,729
Accretion of discount	69,782	13,353	3,352
Net change in income taxes	(372,146)	(212,085)
Changes in timing and other	6,055	(4,709)	8,547
December 31,	1,319,471	485,735	133,530
Extensions [Member]
Supplemental Oil And Gas Reserve Information [Line Items]
Proved oil and gas reserves increase	989,697	426,824	71,333
Discoveries [Member]
Supplemental Oil And Gas Reserve Information [Line Items]
Proved oil and gas reserves increase

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The increase in the net discounted value of the proved oil and gas reserves due only to the passage of time.

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The change in the discounted value of the proved oil and gas reserves due to financial transactions where reserves (minerals in place) were sold.

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This is the amount that proved oil and gas reserves increased due to extensions (increased estimates in the size of proven reserves), discoveries, additions, and improved recovery (increase in ability to extract oil and gas from existing reserves).

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The increase (decrease) in the evaluation or calculation of the costs that will be required in future periods to make it possible to extract or process proved oil and gas reserves.

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The increase (decrease) in the estimate of future income taxes that will be due on future pretax net cash flows relating to the enterprise's proved oil and gas reserves.

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The change in the discounted value of the proved oil and gas reserves due to financial transactions where new reserves were purchased.

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The increase (decrease) in sales and transfer prices and in production (lifting) costs related to future production. The effects of changes in prices and costs are computed before the effects of changes in quantities.

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The actual costs incurred during the reporting period to make it possible to extract or process proved oil and gas reserves. These costs were previously estimated and reduced the estimate of discounted future cash flows from oil and gas reserves.

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Any changes made during the period to the evaluation or calculation of the estimated quantity of oil or gas in proved reserves.

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The amount of sales or transfers of oil gas that was previously included in proved oil and gas reserves. This amount is net of production costs.

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Changes in the standardized measure of discounted future net cash flows relating to proved oil and gas reserves that are not otherwise specified in the taxonomy.

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The balance as of the balance sheet date of the standardized measure of discounted future net cash flow relating to proved oil and gas reserves.

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