Exploratory Costs (Capitalized Exploratory Well Costs) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014 well	Dec. 31, 2013	Dec. 31, 2012
Increase (Decrease) in Capitalized Exploratory Well Costs that are Pending Determination of Proved Reserves [Roll Forward]
Capitalized exploratory well costs at beginning of period	$ 57,600	$ 79,791	$ 70,437
Additions pending determination of proved reserves	946,751	421,599	406,226
Reclassifications due to determination of proved reserves	(882,254)	(442,909)	(396,872)
Exploratory well costs charged to expense	(2,658)	(881)	0
Capitalized exploratory well costs at end of period	119,439	57,600	79,791
Exploratory wells in progress	18,781	14,794
Capitalized exploratory well costs for a period of one year or less	100,658	42,481
Capitalized exploratory well costs for a period greater than one year	0	1,206
Total capitalized exploratory well costs	$ 119,439us-gaap_CapitalizedExploratoryWellCosts	$ 58,481us-gaap_CapitalizedExploratoryWellCosts
Wells in process of drilling	38us-gaap_WellsInProcessOfDrilling

Capitalized Exploratory Well Costs including Wells Expensed in Current Year

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- Definition

Capitalized costs of which include those incurred to (1) drill and equip wells that are not yet completed (2) acquire or construct equipment and facilities that are not yet installed.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 932

-SubTopic 235

-Section 50

-Paragraph 13

-URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e61901-109447

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-Publisher FASB

-Name Accounting Standards Codification

-Glossary Uncompleted Wells, Equipment, and Facilities

-URI http://asc.fasb.org/extlink&oid=6527447

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- Definition

Additions to capitalized exploratory well costs that were added during the reporting period pending the determination of proved reserves.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

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- Definition

Capitalized exploratory well costs that were expensed during the year because proved reserves were not found at the exploratory well.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 932

-SubTopic 235

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- Definition

The amount of capitalized exploratory well costs that is pending the determination of proved reserves. This does not include amounts that were capitalized and subsequently expensed in the same annual period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 932

-SubTopic 235

-Section 50

-Paragraph 1B

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- Definition

The amount of exploratory well costs that have been capitalized for a period of greater than one year after the completion of drilling.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 932

-SubTopic 235

-Section 50

-Paragraph 1B

-Subparagraph b

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- Definition

The amount of exploratory well costs that have been capitalized for a period of one year or less after the completion of drilling.

+ References

No definition available.

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- Definition

Previously capitalized costs of the drilling of wells that were reclassified as part of the costs of the enterprise's wells and related equipment and facilities at the time that proved reserves were found.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 932

-SubTopic 235

-Section 50

-Paragraph 1B

-Subparagraph (a)(2)

-URI http://asc.fasb.org/extlink&oid=8451039&loc=SL6806780-109447

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- Definition

The number of wells in the process of being drilled in each geographic area as of the date listed.

+ References

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

-Publisher SEC

-Name Industry Guide

-Number 2

-Paragraph 7

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