Annual report pursuant to Section 13 and 15(d)

Supplemental Information on Oil and Gas Producing Activities - Standardized Measure of Discounted Future Net Cash Flows Relating to Proved Oil Reserves (Detail)

v2.4.1.9
Supplemental Information on Oil and Gas Producing Activities - Standardized Measure of Discounted Future Net Cash Flows Relating to Proved Oil Reserves (Detail) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Standardized Measure of Discounted Future Net Cash Flows Relating to Proved Oil Reserves        
Future cash inflows $ 823,657us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesCashInflows $ 733,761us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesCashInflows $ 784,906us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesCashInflows  
Future production costs (308,806)us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesProductionCosts (226,681)us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesProductionCosts (206,684)us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesProductionCosts  
Future development costs (136,137)us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesDevelopmentCosts (164,142)us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesDevelopmentCosts (186,982)us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesDevelopmentCosts  
Future income tax expense (178,283)us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesIncomeTaxExpense (155,344)us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesIncomeTaxExpense (182,001)us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesIncomeTaxExpense  
Future net cash flows 200,431us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesNetCashFlows 187,594us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesNetCashFlows 209,239us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesNetCashFlows  
Discount to present value at 10% annual rate (51,044)us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesTenPercentAnnualDiscountForEstimatedTimingOfCashFlows (50,158)us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesTenPercentAnnualDiscountForEstimatedTimingOfCashFlows (56,337)us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesTenPercentAnnualDiscountForEstimatedTimingOfCashFlows  
Standardized measure of discounted future net cash flows 149,387us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves 137,436us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves 152,902us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves 166,187us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves
United States        
Standardized Measure of Discounted Future Net Cash Flows Relating to Proved Oil Reserves        
Future cash inflows 9,598us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesCashInflows
/ us-gaap_StatementGeographicalAxis
= country_US
8,276us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesCashInflows
/ us-gaap_StatementGeographicalAxis
= country_US
8,260us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesCashInflows
/ us-gaap_StatementGeographicalAxis
= country_US
 
Future production costs (1,475)us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesProductionCosts
/ us-gaap_StatementGeographicalAxis
= country_US
(3,038)us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesProductionCosts
/ us-gaap_StatementGeographicalAxis
= country_US
(3,194)us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesProductionCosts
/ us-gaap_StatementGeographicalAxis
= country_US
 
Future income tax expense (359)us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesIncomeTaxExpense
/ us-gaap_StatementGeographicalAxis
= country_US
(825)us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesIncomeTaxExpense
/ us-gaap_StatementGeographicalAxis
= country_US
(807)us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesIncomeTaxExpense
/ us-gaap_StatementGeographicalAxis
= country_US
 
Future net cash flows 7,764us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesNetCashFlows
/ us-gaap_StatementGeographicalAxis
= country_US
4,413us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesNetCashFlows
/ us-gaap_StatementGeographicalAxis
= country_US
4,259us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesNetCashFlows
/ us-gaap_StatementGeographicalAxis
= country_US
 
Discount to present value at 10% annual rate (3,516)us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesTenPercentAnnualDiscountForEstimatedTimingOfCashFlows
/ us-gaap_StatementGeographicalAxis
= country_US
(1,299)us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesTenPercentAnnualDiscountForEstimatedTimingOfCashFlows
/ us-gaap_StatementGeographicalAxis
= country_US
(1,028)us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesTenPercentAnnualDiscountForEstimatedTimingOfCashFlows
/ us-gaap_StatementGeographicalAxis
= country_US
 
Standardized measure of discounted future net cash flows 4,248us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves
/ us-gaap_StatementGeographicalAxis
= country_US
3,114us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves
/ us-gaap_StatementGeographicalAxis
= country_US
3,231us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves
/ us-gaap_StatementGeographicalAxis
= country_US
 
International        
Standardized Measure of Discounted Future Net Cash Flows Relating to Proved Oil Reserves        
Future cash inflows 814,059us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesCashInflows
/ us-gaap_StatementGeographicalAxis
= egy_InternationalMember
725,485us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesCashInflows
/ us-gaap_StatementGeographicalAxis
= egy_InternationalMember
776,646us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesCashInflows
/ us-gaap_StatementGeographicalAxis
= egy_InternationalMember
 
Future production costs (307,331)us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesProductionCosts
/ us-gaap_StatementGeographicalAxis
= egy_InternationalMember
(223,643)us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesProductionCosts
/ us-gaap_StatementGeographicalAxis
= egy_InternationalMember
(203,490)us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesProductionCosts
/ us-gaap_StatementGeographicalAxis
= egy_InternationalMember
 
Future development costs (136,137)us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesDevelopmentCosts
/ us-gaap_StatementGeographicalAxis
= egy_InternationalMember
(164,142)us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesDevelopmentCosts
/ us-gaap_StatementGeographicalAxis
= egy_InternationalMember
(186,982)us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesDevelopmentCosts
/ us-gaap_StatementGeographicalAxis
= egy_InternationalMember
 
Future income tax expense (177,924)us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesIncomeTaxExpense
/ us-gaap_StatementGeographicalAxis
= egy_InternationalMember
(154,519)us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesIncomeTaxExpense
/ us-gaap_StatementGeographicalAxis
= egy_InternationalMember
(181,194)us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesIncomeTaxExpense
/ us-gaap_StatementGeographicalAxis
= egy_InternationalMember
 
Future net cash flows 192,667us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesNetCashFlows
/ us-gaap_StatementGeographicalAxis
= egy_InternationalMember
183,181us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesNetCashFlows
/ us-gaap_StatementGeographicalAxis
= egy_InternationalMember
204,980us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesNetCashFlows
/ us-gaap_StatementGeographicalAxis
= egy_InternationalMember
 
Discount to present value at 10% annual rate (47,528)us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesTenPercentAnnualDiscountForEstimatedTimingOfCashFlows
/ us-gaap_StatementGeographicalAxis
= egy_InternationalMember
(48,859)us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesTenPercentAnnualDiscountForEstimatedTimingOfCashFlows
/ us-gaap_StatementGeographicalAxis
= egy_InternationalMember
(55,309)us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesTenPercentAnnualDiscountForEstimatedTimingOfCashFlows
/ us-gaap_StatementGeographicalAxis
= egy_InternationalMember
 
Standardized measure of discounted future net cash flows $ 145,139us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves
/ us-gaap_StatementGeographicalAxis
= egy_InternationalMember
$ 134,322us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves
/ us-gaap_StatementGeographicalAxis
= egy_InternationalMember
$ 149,671us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves
/ us-gaap_StatementGeographicalAxis
= egy_InternationalMember