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Supplemental Information On Oil And Gas Producing Activities (Narrative) (Detail) | 12 Months Ended |
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Dec. 31, 2015 USD ($) $ / Boe $ / Mcfe MMcf MBbls | Dec. 31, 2014 USD ($) MMcf MBbls | Dec. 31, 2013 USD ($) MMcf MBbls | Dec. 31, 2012 MMcf MBbls
Costs Incurred Oil And Gas Property Acquisition Exploration And Development Activities [Line Items] |  |  |  |  |
Years of production lost due to lower oil prices |  | 3 years 6 months |  |  |
Lower Oil Prices [Member] |  |  |  |  |
Costs Incurred Oil And Gas Property Acquisition Exploration And Development Activities [Line Items] |  |  |  |  |
Revisions of previous estimates |  | 2,705 |  |  |
Removal Of Sour Reserves [Member] |  |  |  |  |
Costs Incurred Oil And Gas Property Acquisition Exploration And Development Activities [Line Items] |  |  |  |  |
Revisions of previous estimates |  | 1,440 |  |  |
Exceeding Expectations [Member] |  |  |  |  |
Costs Incurred Oil And Gas Property Acquisition Exploration And Development Activities [Line Items] |  |  |  |  |
Revisions of previous estimates |  | 370 |  |  |
Oil [Member] |  |  |  |  |
Costs Incurred Oil And Gas Property Acquisition Exploration And Development Activities [Line Items] |  |  |  |  |
Proved Developed Reserves |  | 2,855 | 3,224 | 3,305 | 3,750
Revisions of previous estimates |  | (3,746) | 2,312 | 771 |
Proved reserves |  | 2,855 | 8,260 | 7,232 | 7,488
Gas [Member] |  |  |  |  |
Costs Incurred Oil And Gas Property Acquisition Exploration And Development Activities [Line Items] |  |  |  |  |
Proved Developed Reserves | MMcf |  | 1,053 | 1,406 | 1,333 | 1,544
Revisions of previous estimates | MMcf | [1] | (172) | 300 | 114 |
Proved reserves | MMcf | [1] | 1,053 | 1,406 | 1,333 | 1,544
Consortium [Member] |  |  |  |  |
Costs Incurred Oil And Gas Property Acquisition Exploration And Development Activities [Line Items] |  |  |  |  |
Cost account recovery percentage |  | 70.00% |  |  |
Net cost account | $ |  | $ 87,900,000 |  |  |
Consortium [Member] | Minimum [Member] |  |  |  |  |
Costs Incurred Oil And Gas Property Acquisition Exploration And Development Activities [Line Items] |  |  |  |  |
Profit oil payment percentage |  | 50.00% |  |  |
Consortium [Member] | Maximum [Member] |  |  |  |  |
Costs Incurred Oil And Gas Property Acquisition Exploration And Development Activities [Line Items] |  |  |  |  |
Profit oil payment percentage |  | 60.00% |  |  |
Gabon [Member] |  |  |  |  |
Costs Incurred Oil And Gas Property Acquisition Exploration And Development Activities [Line Items] |  |  |  |  |
Fixed royalty rate |  | 13.00% |  |  |
Gabon [Member] | Oil [Member] |  |  |  |  |
Costs Incurred Oil And Gas Property Acquisition Exploration And Development Activities [Line Items] |  |  |  |  |
Average price for reverse estimate | $ / Boe |  | 49.36 |  |  |
United States [Member] |  |  |  |  |
Costs Incurred Oil And Gas Property Acquisition Exploration And Development Activities [Line Items] |  |  |  |  |
Future development costs | $ |  |  | $ 8,000 | $ 113,000 |
United States [Member] | Oil [Member] |  |  |  |  |
Costs Incurred Oil And Gas Property Acquisition Exploration And Development Activities [Line Items] |  |  |  |  |
Average price for reverse estimate | $ / Boe |  | 40.43 |  |  |
United States [Member] | Gas [Member] |  |  |  |  |
Costs Incurred Oil And Gas Property Acquisition Exploration And Development Activities [Line Items] |  |  |  |  |
Average price for reverse estimate | $ / Mcfe |  | 2.35 |  |  |
Avouma and South Tchibala [Member] |  |  |  |  |
Costs Incurred Oil And Gas Property Acquisition Exploration And Development Activities [Line Items] |  |  |  |  |
Period of development |  | 20 years |  |  |
Avouma and South Tchibala [Member] | Better Performance [Member] |  |  |  |  |
Costs Incurred Oil And Gas Property Acquisition Exploration And Development Activities [Line Items] |  |  |  |  |
Revisions of previous estimates |  |  | 1,500 |  |
Etame [Member] |  |  |  |  |
Costs Incurred Oil And Gas Property Acquisition Exploration And Development Activities [Line Items] |  |  |  |  |
Period of development |  | 20 years |  |  |
Etame [Member] | Better Performance [Member] |  |  |  |  |
Costs Incurred Oil And Gas Property Acquisition Exploration And Development Activities [Line Items] |  |  |  |  |
Revisions of previous estimates |  |  | 1,100 |  |
Etame [Member] | Revised For 2014 [Member] |  |  |  |  |
Costs Incurred Oil And Gas Property Acquisition Exploration And Development Activities [Line Items] |  |  |  |  |
Revisions of previous estimates |  |  |  | 800 |
Ebouri [Member] |  |  |  |  |
Costs Incurred Oil And Gas Property Acquisition Exploration And Development Activities [Line Items] |  |  |  |  |
Period of development |  | 20 years |  |  |
Ebouri [Member] | Uneconomic [Member] |  |  |  |  |
Costs Incurred Oil And Gas Property Acquisition Exploration And Development Activities [Line Items] |  |  |  |  |
Revisions of previous estimates |  |  | 300 |  |
Mutamba Iroru [Member] |  |  |  |  |
Costs Incurred Oil And Gas Property Acquisition Exploration And Development Activities [Line Items] |  |  |  |  |
Cost account recovery percentage |  | 70.00% |  |  |
Proved reserves |  | 0 |  |  |
Block 5 Production [Member] |  |  |  |  |
Costs Incurred Oil And Gas Property Acquisition Exploration And Development Activities [Line Items] |  |  |  |  |
Cost account recovery percentage |  | 50.00% |  |  |
Proved reserves |  | 0 |  |  |
Period of development |  | 20 years |  |  |
Royalty Payments | $ |  | $ 0 |  |  |
Block P Production [Member] |  |  |  |  |
Costs Incurred Oil And Gas Property Acquisition Exploration And Development Activities [Line Items] |  |  |  |  |
Cost account recovery percentage |  | 70.00% |  |  |
Proved reserves |  | 0 |  |  |
Period of development |  | 25 years |  |  |
Income tax on net profits |  | 25.00% |  |  |
Block P Production [Member] | Minimum [Member] |  |  |  |  |
Costs Incurred Oil And Gas Property Acquisition Exploration And Development Activities [Line Items] |  |  |  |  |
Fixed royalty rate |  | 10.00% |  |  |
Profit oil payment percentage |  | 10.00% |  |  |
Block P Production [Member] | Maximum [Member] |  |  |  |  |
Costs Incurred Oil And Gas Property Acquisition Exploration And Development Activities [Line Items] |  |  |  |  |
Fixed royalty rate |  | 16.00% |  |  |
Profit oil payment percentage |  | 60.00% |  |  |
[1] | The natural gas reserves shown as of December 31, 2015 include natural gas liquids ("NGL") expressed as gas volumes using a ratio of 4.9 MMcf to 1 MBbl of NGL.

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