Annual report pursuant to Section 13 and 15(d)

Income Taxes (Income Tax Years Subject To Examination By Major Tax Jurisdictions) (Details)

v3.10.0.1
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