Property, Plant And Equipment (Net Changes in Capitalized Exploratory Well Costs) (Details) (USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Property, Plant And Equipment [Abstract]
Beginning balance at January 1	$ 393,030,000us-gaap_CapitalizedExploratoryWellCosts	$ 445,697,000us-gaap_CapitalizedExploratoryWellCosts	$ 556,412,000us-gaap_CapitalizedExploratoryWellCosts
Additions pending the determination of proved reserves	2,874,000	57,716,000	135,849,000
Reclassifications to proved properties based on the determination of proved reserves	(91,236,000)	(93,936,000)	(165,377,000)
Reduction of capitalized exploratory well costs due to partial asset sale	(122,175,000)
Capitalized exploratory well costs charged to expense	(62,038,000)	(16,447,000)	(81,187,000)
Ending balance at December 31	$ 120,455,000us-gaap_CapitalizedExploratoryWellCosts	$ 393,030,000us-gaap_CapitalizedExploratoryWellCosts	$ 445,697,000us-gaap_CapitalizedExploratoryWellCosts

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

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)(1)

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

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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

-Section 50

-Paragraph 1B

-Subparagraph (a)(3)

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

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- Definition

The change during the reporting period in capitalized exploratory well costs. This change comprises additions of capitalized costs where proven reserves have not been found, reclassification of capitalized costs where proved reserves were found, and capitalized costs that were expensed when proved reserves were definitively not 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

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

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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

-Subparagraph (a)

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

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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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