Supplemental Information On Oil And Gas Producing Activities (Narrative) (Detail)		12 Months Ended
		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.