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Subsequent Events (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Apr. 03, 2012 Amended Credit Facility [Member]	Oct. 06, 2011 Amended Credit Facility [Member]	Feb. 02, 2011 Amended Credit Facility [Member]	May 01, 2012 2012 Two-Way And Three-Way Collars [Member]	May 01, 2012 2013 Two-Way And Three-Way Collars [Member]	May 01, 2012 2014 Two-Way And Three-Way Collars [Member]	May 01, 2012 2015 Two-Way And Three-Way Collars [Member]
Subsequent Event [Line Items]
Term of contract	1
Line of credit facility amount outstanding		$ 500.0	$ 350.0	$ 137.5
Total notional amount, in barrels					306,000	730,000	730,000	62,000

X

- Definition

Aggregate notional amount of derivative expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 12

+ Details

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Namespace Prefix:	invest_
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Balance Type:	na
Period Type:	instant

X

- Definition

Minimum initial term of contracts disclosed.

+ References

No definition available.

+ Details

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X

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 129

-Paragraph 2, 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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5



Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(b),22(b))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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