Supplemental Oil and Gas Disclosures (Principal Sources Chg SM) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Increase Decrease In Standardized Measure Of Discounted Future Net Cash Flow Relating To ProvedOil And Gas Reserves RollForward
Standarized measure, beginning of period	$ 264,872	$ 111,297	$ 55,698
Net changes in prices and production costs	(33,520)	147,776	86,915
Future development costs incurred	172,462	76,721	21,112
Net changes in estimated future development costs	(193,359)	(9,261)	(48,356)
Revisions Of Previous Quantity Estimates	(56,525)	(36,421)	16,375
Extensions and discoveries	102,386	68,452	110,059
Accretion Of Discount	42,589	18,801	2,630
Changes in income taxes, net	(74,778)	(136,157)	(35,306)
Sale of oil and gas produced, net of production costs	(165,547)	(44,556)	(56,327)
Purchased reserves	457,033	26,340	2,386
Sales of reserves in place	(6,971)	0	(48,310)
Change in production, timing and other	(9,664)	41,880	4,421
Standarized measure, end of period	$ 498,978	$ 264,872	$ 111,297

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 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 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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