Segment Information (Reconciliation of Segment Profit to Operating Income) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Segment Reporting [Abstract]
Segment Profits	$ 64,194	$ 62,833	$ 195,873	$ 196,270
General and administrative	(17,349)	(14,331)	(46,729)	(40,084)
Gain (loss) on derivatives	(759)	(563)	1,977	(5,520)
Gain (loss) sale of property	(109)	(397)	395	(317)
Depreciation, amortization, and impairments	(45,078)	(31,930)	(110,163)	(93,257)
Operating Income Loss	$ 899	$ 15,612	$ 41,353	$ 57,092

Aggregate net gain (loss) on all derivative instruments recognized in earnings during the period, before tax effects.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4A

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5618551-113959

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The gains (losses) included in results of operations resulting from the sale or disposal of property, plant and equipment, which do not qualify for treatment as discontinued operations. This item does not include any gain (loss) recognized on the sale of oil and gas property or timber property.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 144

-Paragraph 37, 41, 42, 43, 45

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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The aggregate total of expenses of managing and administering the affairs of an entity, including affiliates of the reporting entity, which are not directly or indirectly associated with the manufacture, sale or creation of a product or product line.

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

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-Name Accounting Standards Codification

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-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.4)

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The net result for the period of deducting operating expenses from operating revenues.

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The aggregate expense recognized in the current period that allocates the cost of tangible assets, intangible assets,depleting assets, and impairments to periods that benefit from use of the assets.

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Amount of profit or loss recognized by the reportable segment.

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