Disclosure About Oil and Gas Producing Activities (Unaudited) (Details 4) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Oil And Gas Exploration And Production Industries Disclosures [Abstract]
Acquisition costs - unproved properties	$ 26,106	$ 424,540	$ 47,979
Acquisition costs - proved properties	895,179	224,410	0
Exploration	197,664us-gaap_CostsIncurredExplorationCosts	184,007us-gaap_CostsIncurredExplorationCosts	199,569us-gaap_CostsIncurredExplorationCosts
Development	382,984us-gaap_CostsIncurredDevelopmentCosts	186,755us-gaap_CostsIncurredDevelopmentCosts	587,618us-gaap_CostsIncurredDevelopmentCosts
Total	$ 1,501,933	$ 1,019,712	$ 835,166

Costs incurred, including capitalized costs and costs charged to expense, associated with the acquisition of oil and gas properties that have proved reserves.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 932

-SubTopic 235

-Section 50

-Paragraph 19

-URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62038-109447

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

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Costs incurred, including capitalized costs and costs charged to expense, associated with the acquisition of oil and gas properties that have unproved reserves.

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Development costs incurred, including capitalized costs and costs charged to expense, in oil and gas activities.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 932

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Exploration costs incurred, including capitalized costs and costs charged to expense, in oil and gas activities.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Exploration

-URI http://asc.fasb.org/extlink&oid=6512329

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-Publisher FASB

-Name Accounting Standards Codification

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Amount of costs incurred related to oil and gas property acquisition, exploration and development activities, including capitalized costs and costs charged to expense.

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