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Summary of Significant Accounting Policies - Narrative (Details) (USD $) | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2011
Summary Of Significant Accounting Policies [Line Items] |  |  |  |
Accounts receivable, collection period | 30 days |  |  |
Conversion ratio, gas to barrels of oil | 6 gpor_ConversionRatioGasToBarrelsOfOil |  |  |
Capitalized costs of oil and natural gas properties excluded from amortization | $ 1,465,538,000 us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationCumulative | $ 1,020,835,000 us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationCumulative |  |
Cumulative translation adjustment | (26,675,000)us-gaap_AccumulatedOtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentNetOfTax | (9,781,000)us-gaap_AccumulatedOtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentNetOfTax | 2,442,000 us-gaap_AccumulatedOtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentNetOfTax | 1,087,000 us-gaap_AccumulatedOtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentNetOfTax
Minimum [Member] |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |
Useful life | 3 years |  |  |
Maximum [Member] |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |
Vesting period | 5 years |  |  |
Useful life | 30 years |  |  |
Tatex Thailand III LLC [Member] |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |
Equity Method Investment, Other than Temporary Impairment | $ 12,100,000 us-gaap_EquityMethodInvestmentOtherThanTemporaryImpairment / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_TatexThailandIiiLlcMember | $ 0 us-gaap_EquityMethodInvestmentOtherThanTemporaryImpairment / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_TatexThailandIiiLlcMember |  |
Restricted Stock [Member] | Minimum [Member] |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |
Vesting period | 1 year |  |  |
Restricted Stock [Member] | Maximum [Member] |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |
Vesting period | 5 years |  |  |
Customer Concentration Risk [Member] | Accounts Receivable [Member] |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |
Concentration Risk, Number of Purchasers | 3 gpor_ConcentrationRiskNumberofPurchasers / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_AccountsReceivableMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember |  |  |

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- Definition Accumulated adjustment, net of tax, that results from the process of translating subsidiary financial statements and foreign equity investments into the reporting currency from the functional currency of the reporting entity, net of reclassification of realized foreign currency translation gains or losses. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -URI http://asc.fasb.org/extlink&oid=28358780&loc=SL7669686-108580 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=28358780&loc=d3e637-108580 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14 -URI http://asc.fasb.org/extlink&oid=28358780&loc=d3e681-108580 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=28358780&loc=SL7669646-108580 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 830 -SubTopic 30 -Section 45 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=6915805&loc=d3e32022-110900 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 830 -SubTopic 30 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6450520&loc=d3e32583-110901 + Details
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