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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
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Standardized Measure of Discounted Future Net Cash Flows Relating to Proved Oil Reserves |  |  |  |
Future cash inflows | $ 823,657 us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesCashInflows | $ 733,761 us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesCashInflows | $ 784,906 us-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 | 200,431 us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesNetCashFlows | 187,594 us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesNetCashFlows | 209,239 us-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 | 149,387 us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves | 137,436 us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves | 152,902 us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves | 166,187 us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves
United States |  |  |  |
Standardized Measure of Discounted Future Net Cash Flows Relating to Proved Oil Reserves |  |  |  |
Future cash inflows | 9,598 us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesCashInflows / us-gaap_StatementGeographicalAxis = country_US | 8,276 us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesCashInflows / us-gaap_StatementGeographicalAxis = country_US | 8,260 us-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 | 7,764 us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesNetCashFlows / us-gaap_StatementGeographicalAxis = country_US | 4,413 us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesNetCashFlows / us-gaap_StatementGeographicalAxis = country_US | 4,259 us-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 | 4,248 us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves / us-gaap_StatementGeographicalAxis = country_US | 3,114 us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves / us-gaap_StatementGeographicalAxis = country_US | 3,231 us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves / us-gaap_StatementGeographicalAxis = country_US |
International |  |  |  |
Standardized Measure of Discounted Future Net Cash Flows Relating to Proved Oil Reserves |  |  |  |
Future cash inflows | 814,059 us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesCashInflows / us-gaap_StatementGeographicalAxis = egy_InternationalMember | 725,485 us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesCashInflows / us-gaap_StatementGeographicalAxis = egy_InternationalMember | 776,646 us-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 | 192,667 us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesNetCashFlows / us-gaap_StatementGeographicalAxis = egy_InternationalMember | 183,181 us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesNetCashFlows / us-gaap_StatementGeographicalAxis = egy_InternationalMember | 204,980 us-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 | $ 145,139 us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves / us-gaap_StatementGeographicalAxis = egy_InternationalMember | $ 134,322 us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves / us-gaap_StatementGeographicalAxis = egy_InternationalMember | $ 149,671 us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves / us-gaap_StatementGeographicalAxis = egy_InternationalMember |

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- Definition Amount of estimated future accumulated cash inflow from the sale of proved oil and gas reserves. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 30 -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62424-109447 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 31 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62455-109447 + Details
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- Definition Amount of estimated future accumulated cash outflow for costs to be incurred in developing proved oil and gas reserves. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 30 -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62424-109447 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 31 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62455-109447 + Details
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- Definition Amount of estimated future accumulated cash outflow for income tax, based on the future income less future expense derived from production and sale of proved oil and gas reserves. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 30 -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62424-109447 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 31 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62455-109447 + Details
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- Definition Amount, after future accumulated cash outflow for development and production costs and future income tax, of estimated future accumulated cash inflow from the sale of proved oil and gas reserves. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 30 -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62424-109447 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 31 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62455-109447 + Details
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- Definition Amount of discount on future accumulated cash inflow, after deducting future accumulated cash outflow for development and production costs and future income tax, from sale of proved oil and gas reserves, using a discount rate of ten percent a year. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 30 -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62424-109447 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 31 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62455-109447 + Details
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