Derivative Instruments and Hedging Activities (Derivatives By Balance Sheet Location) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Derivatives, Fair Value [Line Items]
Derivative assets - current	$ 9,915	$ 19,477
Derivative assets - long-term	18,712	36
Derivative liabilities - current	(1,895)	(2,842)
Derivative liabilities - long-term	(87)	(23,781)
Total derivatives not designated as hedging instruments	26,645	(7,110)
Crude Oil Contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative assets - current	9,915	19,477
Derivative assets - long-term	18,712	36
Derivative liabilities - current	(1,895)	(2,659)
Derivative liabilities - long-term	(87)	(23,781)
Deferred Premiums [Member]
Derivatives, Fair Value [Line Items]
Derivative liabilities - current	$ 0	$ (183)

Carrying amount as of the balance sheet date of the asset arising from commodity contracts such as futures contracts tied to the movement of a particular commodity, which are expected to be converted into cash or otherwise disposed of within a year or the normal operating cycle, if longer.

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Carrying amount as of the balance sheet date of the asset arising from commodity contracts such as futures contracts tied to the movement of a particular commodity, which are expected to be converted into cash or otherwise disposed of after a year or beyond the normal operating cycle, if longer.

+ References

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Fair values as of the balance sheet date of the net amount of all assets and liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 107

-Paragraph 10

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-Topic 815

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Carrying amount as of the balance sheet date of the liability arising from a financial instrument or a contract used to mitigate a specified risk (hedge), and which are expected to be converted into cash or otherwise disposed of within a year or the normal operating cycle, if longer.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

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-Publisher AICPA

-Name Audit and Accounting Guide (AAG)

-Number AAG-BRD

-Paragraph 41

-IssueDate 2006-05-01

-Chapter 7

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Fair value of liability arising from a financial instrument or contract used to mitigate a specified risk (hedge), expected to be settled after one year or beyond the normal operating cycle, if longer.

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-Name Accounting Standards Codification

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