Annual report pursuant to Section 13 and 15(d)

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

v3.3.1.900
Income Taxes (Income Tax Years Subject To Examination By Major Tax Jurisdictions) (Detail)
12 Months Ended
Dec. 31, 2015
United States [Member] | Minimum [Member]  
Income Tax Examination [Line Items]  
Income tax examination year under examination 2008
United States [Member] | Maximum [Member]  
Income Tax Examination [Line Items]  
Income tax examination year under examination -2015
Gabon [Member] | Minimum [Member]  
Income Tax Examination [Line Items]  
Income tax examination year under examination 2007
Gabon [Member] | Maximum [Member]  
Income Tax Examination [Line Items]  
Income tax examination year under examination -2015