Acquisitions and Divestitures (Details) (Riley Ridge [Member], USD $)	Oct. 15, 2010
Riley Ridge [Member]
Riley Ridge Purchase Price Allocation
Oil and natural gas properties	$ 19,646,000
CO2 and other non-hydrocarbon gases properties	10,907,000
Pipelines and plants	72,070,000
Prepaid construction and drilling costs	9,346,000
Other assets	19,300,000
Asset retirement obligations	(472,000)
Goodwill	1,460,000
Assets Acquired (Liabilities Assumed), Total	$ 132,257,000

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Amount of cash paid to acquire the entity.

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The amount of acquisition cost of a business combination allocated to prepaid expenses and other current assets. Does not include amounts allocated to cash and cash equivalents, marketable securities, receivables, inventory, and assets not to be used.

+ References

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Amount of goodwill arising from a business combination, which is the excess of the cost of the acquired entity over the amounts assigned to assets acquired and liabilities assumed.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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The amount of acquisition cost of a business combination allocated to mineral rights for acquired entities in the mining industry.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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The amount of acquisition cost of a business combination allocated to natural resources other than mineral rights in the mining industry.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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The amount of acquisition cost of a business combination allocated to other noncurrent liabilities of the acquired entity.

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The amount of acquisition cost of a business combination allocated to a plant used in the normal course of business, not including a plant that is held-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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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-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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