Property, Plant And Equipment (Net Changes in Capitalized Exploratory Well Costs) (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Property, Plant And Equipment [Abstract]
Beginning balance at January 1	$ 207,855	$ 155,103
Additions pending the determination of proved reserves	32,416	549
Capitalized exploratory well costs charged to expense	(13,145)	0
Ending balance at December 31	$ 227,126	$ 155,652

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=68064819&loc=SL6806780-109447

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of expense for capitalized exploratory well costs for which 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=68064819&loc=SL6806780-109447

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Period Type:	duration

- 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=68064819&loc=SL6806780-109447

+ Details

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Balance Type:	debit
Period Type:	instant

- References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration