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Income Taxes (Income Tax Years Subject To Examination By Major Tax Jurisdictions) (Details)	12 Months Ended
	Dec. 31, 2017
U.S. [Member] | Minimum [Member]
Income Tax Examination [Line Items]
Income tax examination year under examination	2008
U.S. [Member] | Maximum [Member]
Income Tax Examination [Line Items]
Income tax examination year under examination	2017
Gabon [Member] | Minimum [Member]
Income Tax Examination [Line Items]
Income tax examination year under examination	2013
Gabon [Member] | Maximum [Member]
Income Tax Examination [Line Items]
Income tax examination year under examination	2017

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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- Definition

Tax year being audited in the income tax examination, in CCYY format.

+ References

No definition available.

+ Details

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