Annual report pursuant to Section 13 and 15(d)

Supplemental Information on Oil and Gas Producing Activities - Results of Operations for Oil and Gas Producing Activities (Detail)

v2.4.1.9
Supplemental Information on Oil and Gas Producing Activities - Results of Operations for Oil and Gas Producing Activities (Detail) (USD $)
In Thousands, unless otherwise specified
 3 Months Ended 12 Months Ended
Dec. 31, 2014
Sep. 30, 2014
Jun. 30, 2014
Mar. 31, 2014
Dec. 31, 2013
Sep. 30, 2013
Jun. 30, 2013
Mar. 31, 2013
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Results of Operations for Oil and Gas Producing Activities:                      
Crude oil and gas sales $ 23,037us-gaap_OilAndGasSalesRevenue [1] $ 24,486us-gaap_OilAndGasSalesRevenue [1] $ 52,098us-gaap_OilAndGasSalesRevenue [1] $ 28,071us-gaap_OilAndGasSalesRevenue [1] $ 58,282us-gaap_OilAndGasSalesRevenue [1] $ 37,740us-gaap_OilAndGasSalesRevenue [1] $ 29,118us-gaap_OilAndGasSalesRevenue [1] $ 44,137us-gaap_OilAndGasSalesRevenue [1] $ 127,691us-gaap_OilAndGasSalesRevenue $ 169,277us-gaap_OilAndGasSalesRevenue $ 195,287us-gaap_OilAndGasSalesRevenue
United States                      
Results of Operations for Oil and Gas Producing Activities:                      
Crude oil and gas sales                 1,369us-gaap_OilAndGasSalesRevenue
/ us-gaap_StatementGeographicalAxis
= country_US 		1,891us-gaap_OilAndGasSalesRevenue
/ us-gaap_StatementGeographicalAxis
= country_US 		2,798us-gaap_OilAndGasSalesRevenue
/ us-gaap_StatementGeographicalAxis
= country_US
Production, G&A and other expense                 (467)us-gaap_ResultsOfOperationsProductionOrLiftingCosts
/ us-gaap_StatementGeographicalAxis
= country_US 		(12,232)us-gaap_ResultsOfOperationsProductionOrLiftingCosts
/ us-gaap_StatementGeographicalAxis
= country_US 		(47,866)us-gaap_ResultsOfOperationsProductionOrLiftingCosts
/ us-gaap_StatementGeographicalAxis
= country_US
Depreciation, depletion and amortization                 (901)us-gaap_ResultsOfOperationsDepreciationDepletionAndAmortizationAndValuationProvisions
/ us-gaap_StatementGeographicalAxis
= country_US 		(1,528)us-gaap_ResultsOfOperationsDepreciationDepletionAndAmortizationAndValuationProvisions
/ us-gaap_StatementGeographicalAxis
= country_US 		(3,872)us-gaap_ResultsOfOperationsDepreciationDepletionAndAmortizationAndValuationProvisions
/ us-gaap_StatementGeographicalAxis
= country_US
Results from oil and gas producing activities                 1us-gaap_ResultsOfOperationsOilAndGasProducingActivitiesNetIncomeExcludingCorporateOverheadAndInterestCosts
/ us-gaap_StatementGeographicalAxis
= country_US 		(11,869)us-gaap_ResultsOfOperationsOilAndGasProducingActivitiesNetIncomeExcludingCorporateOverheadAndInterestCosts
/ us-gaap_StatementGeographicalAxis
= country_US 		(48,940)us-gaap_ResultsOfOperationsOilAndGasProducingActivitiesNetIncomeExcludingCorporateOverheadAndInterestCosts
/ us-gaap_StatementGeographicalAxis
= country_US
Gabon                      
Results of Operations for Oil and Gas Producing Activities:                      
Crude oil and gas sales                 126,322us-gaap_OilAndGasSalesRevenue
/ us-gaap_StatementGeographicalAxis
= country_GA 		167,386us-gaap_OilAndGasSalesRevenue
/ us-gaap_StatementGeographicalAxis
= country_GA 		192,489us-gaap_OilAndGasSalesRevenue
/ us-gaap_StatementGeographicalAxis
= country_GA
Production, G&A and other expense                 (150,602)us-gaap_ResultsOfOperationsProductionOrLiftingCosts
/ us-gaap_StatementGeographicalAxis
= country_GA 		(52,776)us-gaap_ResultsOfOperationsProductionOrLiftingCosts
/ us-gaap_StatementGeographicalAxis
= country_GA 		(27,425)us-gaap_ResultsOfOperationsProductionOrLiftingCosts
/ us-gaap_StatementGeographicalAxis
= country_GA
Depreciation, depletion and amortization                 (19,079)us-gaap_ResultsOfOperationsDepreciationDepletionAndAmortizationAndValuationProvisions
/ us-gaap_StatementGeographicalAxis
= country_GA 		(15,302)us-gaap_ResultsOfOperationsDepreciationDepletionAndAmortizationAndValuationProvisions
/ us-gaap_StatementGeographicalAxis
= country_GA 		(15,954)us-gaap_ResultsOfOperationsDepreciationDepletionAndAmortizationAndValuationProvisions
/ us-gaap_StatementGeographicalAxis
= country_GA
Income tax                 (22,486)us-gaap_ResultsOfOperationsIncomeTaxExpense
/ us-gaap_StatementGeographicalAxis
= country_GA 		(34,115)us-gaap_ResultsOfOperationsIncomeTaxExpense
/ us-gaap_StatementGeographicalAxis
= country_GA 		(81,813)us-gaap_ResultsOfOperationsIncomeTaxExpense
/ us-gaap_StatementGeographicalAxis
= country_GA
Results from oil and gas producing activities                 $ (65,845)us-gaap_ResultsOfOperationsOilAndGasProducingActivitiesNetIncomeExcludingCorporateOverheadAndInterestCosts
/ us-gaap_StatementGeographicalAxis
= country_GA 		$ 65,193us-gaap_ResultsOfOperationsOilAndGasProducingActivitiesNetIncomeExcludingCorporateOverheadAndInterestCosts
/ us-gaap_StatementGeographicalAxis
= country_GA 		$ 67,297us-gaap_ResultsOfOperationsOilAndGasProducingActivitiesNetIncomeExcludingCorporateOverheadAndInterestCosts
/ us-gaap_StatementGeographicalAxis
= country_GA
[1] Gabon crude oil sales are a function of the number and size of crude oil liftings in each quarter from the floating production, storage and offloading (“FPSO”) facility.