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Summary of Significant Accounting Policies - Inventory (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Inventory Net [Line Items]
Equipment and materials	$ 16,438	$ 2,709
Crude oil inventory	4,269	834
Inventory, net	$ 20,707	$ 3,543

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Carrying amount as of the balance sheet date of petroleum or crude oil.

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Carrying amount (lower of cost or market) as of the balance sheet date of inventories less all valuation and other allowances. Excludes noncurrent inventory balances (expected to remain on hand past one year or one operating cycle, if longer).

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Gross amount of products used directly or indirectly in the manufacturing or production process, which may or may not become part of the final product. May also include items used in the storage, presentation or transportation of physical goods.

+ References

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

-Publisher AICPA

-Name Accounting Research Bulletin (ARB)

-Number 43

-Paragraph 3

-Chapter 4

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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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