Fair Value Measurements (Level 3 Fair Value Measurements) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	6 Months Ended
Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Fair value of Level 3 instruments, beginning of period	$ (6,097)	$ 0	$ 6,709	$ 0
Fair value adjustments on commodity derivatives	(33,019)	3,096	(45,825)	3,096
Fair value of Level 3 instruments, end of period	(39,116)	3,096	(39,116)	3,096
Fair Value, Assets and Liabilities Measured on Recurring Basis, Change in Unrealized Gain (Loss)	$ (33,019)	$ 3,096	$ (45,825)	$ 3,096

Amount of unrealized (holding) gain (loss) which is included in the statement of income (or changes in net assets) related to those assets still held at the reporting date for which fair value is measured on a recurring basis using significant unobservable inputs (Level 3).

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=25499696&loc=d3e19207-110258

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- Definition

Amount of gain (loss) recognized in the income statement of financial instrument classified as a derivative asset (liability) after deduction of derivative liability (asset), measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 3

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=25499696&loc=d3e19279-110258

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=25499696&loc=d3e19207-110258

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- Definition

Fair value of financial instrument classified as derivative asset (liability) after deduction of derivative liability (asset), measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

+ Details

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