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Commitments And Contingencies (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended					1 Months Ended	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 Fracturing Services [Member]	Dec. 31, 2011 Drilling Contracts [Member]	Jan. 31, 2012 Long Term Commitments [Member]	Dec. 31, 2011 Long Term Commitments [Member]	Jan. 31, 2012 Millions Of Barrels [Member] Long Term Commitments [Member]	Dec. 31, 2011 Millions Of Barrels [Member] Long Term Commitments [Member] Williston Basin Project [Member] Volume Commitment Agreements [Member]	Dec. 31, 2011 Billions of Cubic Feet [Member] Long Term Commitments [Member] Williston Basin Project [Member]
Supply Commitment [Line Items]
Rental expense	$ 0.8	$ 0.6	$ 0.4
Payments upon early contract termination				102.4	63.2
Minimum quantity of delivery								4.4	9.6	18.2
Future obligations under supply agreements						$ 13.0	$ 54.5

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Future obligations under supply agreements

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- Definition

The loss recognized on termination of a contract.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 912

-SubTopic 275

-Section 50

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=6471736&loc=d3e54681-109401

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Total amount of product committed to be supplied under existing contracts or agreements.

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

-Publisher SEC

-Name Industry Guide

-Number 2

-Paragraph 8

-Subparagraph A

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- Definition

Rental expense for the reporting period incurred under operating leases, including minimum and any contingent rent expense, net of related sublease income.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 20

-Section 50

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-URI http://asc.fasb.org/extlink&oid=6453985&loc=d3e41499-112717

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