Income Taxes (Income Tax Years Subject To Examination By Major Tax Jurisdictions) (Details)	12 Months Ended
	Dec. 31, 2018
United States | Minimum
Income Tax Examination [Line Items]
Income tax examination year under examination	2009
United States | Maximum
Income Tax Examination [Line Items]
Income tax examination year under examination	2018
Gabon | Minimum
Income Tax Examination [Line Items]
Income tax examination year under examination	2014
Gabon | Maximum
Income Tax Examination [Line Items]
Income tax examination year under examination	2018