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Acquisitions (Details) (USD $) | 1 Months Ended | 3 Months Ended | 12 Months Ended | 0 Months Ended | 9 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | ---
Feb. 28, 2011 | 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 | Nov. 13, 2013 | Feb. 15, 2013 | Jan. 07, 2013 | Dec. 24, 2012 | Mar. 20, 2014 | Dec. 21, 2012 | Dec. 18, 2012 | Dec. 19, 2012 acre | Dec. 24, 2012 acre | Dec. 31, 2014 | May 31, 2013 | Feb. 28, 2014 acre | Dec. 17, 2012 acre
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Period allowed for refusal | 6 months |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Affiliates participation ratio | 50.00%gpor_AffiliatesParticipationInAcquisitionRatio |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount put in escrow |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 10,000,000 us-gaap_EscrowDeposit |  |
Proceeds from issuance of common stock, net of offering costs |  |  |  |  |  |  |  |  |  | 689,000 us-gaap_ProceedsFromIssuanceOfCommonStock | 766,495,000 us-gaap_ProceedsFromIssuanceOfCommonStock | 427,091,000 us-gaap_ProceedsFromIssuanceOfCommonStock |  |  |  |  |  |  |  |  |  |  |  |  |
Net revenues |  | 267,697,000 us-gaap_Revenues | 170,804,000 us-gaap_Revenues | 114,736,000 us-gaap_Revenues | 118,029,000 us-gaap_Revenues | 68,067,000 us-gaap_Revenues | 69,252,000 us-gaap_Revenues | 70,434,000 us-gaap_Revenues | 55,000,000 us-gaap_Revenues | 671,266,000 us-gaap_Revenues | 262,753,000 us-gaap_Revenues | 248,926,000 us-gaap_Revenues |  |  |  |  |  |  |  |  |  |  |  |  |
Lease operating expenses |  |  |  |  |  |  |  |  |  | 52,191,000 us-gaap_LeaseOperatingExpense | 26,703,000 us-gaap_LeaseOperatingExpense | 24,308,000 us-gaap_LeaseOperatingExpense |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock [Member] | Public Offering [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stock option, portion attributable to underwriters (shares) |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 900,000 gpor_StockIssuedDuringPeriodSharesOverAllotmentOptionPortionAttributableToUnderwriters / gpor_SaleOfStockAxis = gpor_PublicOfferingMember / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember | 750,000 gpor_StockIssuedDuringPeriodSharesOverAllotmentOptionPortionAttributableToUnderwriters / gpor_SaleOfStockAxis = gpor_PublicOfferingMember / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember |  |  |  |  |  |  |  |  |
Proceeds from issuance of common stock, net of offering costs |  |  |  |  |  |  |  |  |  |  |  |  | 408,000,000 us-gaap_ProceedsFromIssuanceOfCommonStock / gpor_SaleOfStockAxis = gpor_PublicOfferingMember / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember | 325,800,000 us-gaap_ProceedsFromIssuanceOfCommonStock / gpor_SaleOfStockAxis = gpor_PublicOfferingMember / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember |  | 460,700,000 us-gaap_ProceedsFromIssuanceOfCommonStock / gpor_SaleOfStockAxis = gpor_PublicOfferingMember / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember |  |  |  |  |  |  |  |  |
Utica Shale [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gas and oil acreage, undeveloped, net |  |  |  |  |  |  |  |  |  |  |  |  |  | 22,000 us-gaap_GasAndOilAreaUndevelopedNet / us-gaap_BusinessAcquisitionAxis = gpor_UticaShaleMember |  | 37,000 us-gaap_GasAndOilAreaUndevelopedNet / us-gaap_BusinessAcquisitionAxis = gpor_UticaShaleMember |  |  |  | 7,000 us-gaap_GasAndOilAreaUndevelopedNet / us-gaap_BusinessAcquisitionAxis = gpor_UticaShaleMember | 37,000 us-gaap_GasAndOilAreaUndevelopedNet / us-gaap_BusinessAcquisitionAxis = gpor_UticaShaleMember |  |  | 8,000 us-gaap_GasAndOilAreaUndevelopedNet / us-gaap_BusinessAcquisitionAxis = gpor_UticaShaleMember | 30,000 us-gaap_GasAndOilAreaUndevelopedNet / us-gaap_BusinessAcquisitionAxis = gpor_UticaShaleMember
Cash price of ownership interest |  |  |  |  |  |  |  |  |  |  |  |  |  | 220,000,000 us-gaap_PaymentsToAcquireOilAndGasPropertyAndEquipment / us-gaap_BusinessAcquisitionAxis = gpor_UticaShaleMember |  |  |  | 70,000,000 us-gaap_PaymentsToAcquireOilAndGasPropertyAndEquipment / us-gaap_BusinessAcquisitionAxis = gpor_UticaShaleMember | 302,000,000 us-gaap_PaymentsToAcquireOilAndGasPropertyAndEquipment / us-gaap_BusinessAcquisitionAxis = gpor_UticaShaleMember | 372,000,000 us-gaap_PaymentsToAcquireOilAndGasPropertyAndEquipment / us-gaap_BusinessAcquisitionAxis = gpor_UticaShaleMember |  |  |  |  |
Amount put in escrow |  |  |  |  |  |  |  |  |  |  |  |  |  | 33,600,000 us-gaap_EscrowDeposit / us-gaap_BusinessAcquisitionAxis = gpor_UticaShaleMember |  | 53,900,000 us-gaap_EscrowDeposit / us-gaap_BusinessAcquisitionAxis = gpor_UticaShaleMember |  |  |  |  | 53,900,000 us-gaap_EscrowDeposit / us-gaap_BusinessAcquisitionAxis = gpor_UticaShaleMember |  |  |  |
Proceeds from issuance of common stock, net of offering costs |  |  |  |  |  |  |  |  |  |  |  |  |  | 325,800,000 us-gaap_ProceedsFromIssuanceOfCommonStock / us-gaap_BusinessAcquisitionAxis = gpor_UticaShaleMember |  |  |  |  |  |  | 460,700,000 us-gaap_ProceedsFromIssuanceOfCommonStock / us-gaap_BusinessAcquisitionAxis = gpor_UticaShaleMember |  |  |  |
Existing wells excluded |  |  |  |  |  |  |  |  |  |  |  |  |  | 14 gpor_NumberOfWellsOwned / us-gaap_BusinessAcquisitionAxis = gpor_UticaShaleMember |  |  |  |  |  |  |  |  |  |  |
Future wells excluded |  |  |  |  |  |  |  |  |  |  |  |  |  | 16 gpor_NumberOfProposedFutureWellsExcludedFromAcquisition / us-gaap_BusinessAcquisitionAxis = gpor_UticaShaleMember |  |  |  |  |  |  |  |  |  |  |
Purchase price |  |  |  |  |  |  |  |  |  | 182,000,000 us-gaap_BusinessCombinationConsiderationTransferred1 / us-gaap_BusinessAcquisitionAxis = gpor_UticaShaleMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cash, net of purchase price adjustments |  |  |  |  |  |  |  |  |  | 179,500,000 gpor_PaymenttoAcquireOilandGasPropertyandEquipmentNet / us-gaap_BusinessAcquisitionAxis = gpor_UticaShaleMember |  |  |  |  |  |  | 179,527,000 gpor_PaymenttoAcquireOilandGasPropertyandEquipmentNet / us-gaap_BusinessAcquisitionAxis = gpor_UticaShaleMember |  |  |  |  |  |  |  |
Net revenues |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 6,400,000 us-gaap_Revenues / us-gaap_BusinessAcquisitionAxis = gpor_UticaShaleMember |  |  |
Lease operating expenses |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1,000,000 us-gaap_LeaseOperatingExpense / us-gaap_BusinessAcquisitionAxis = gpor_UticaShaleMember |  |  |

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- Definition Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 30 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=6911251&loc=d3e6578-128477 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 30 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=6911251&loc=d3e6613-128477 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=7488404&loc=d3e6927-128479 + Details
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- Definition The designation of funds furnished by a borrower to a lender to assure future payments of the borrower's real estate taxes and insurance obligations with respect to a mortgaged property. Escrow deposits may be made for a variety of other purposes such as earnest money and contingent payments. This element excludes replacement reserves which are an escrow separately provided for within the US GAAP taxonomy. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.10) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
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- Definition Fractional interest owned based on working interests or other economic arrangements of lease area on which wells have not been drilled or completed to a point that would permit the production of commercial quantities of oil and gas regardless of whether or not such area contains proved reserves. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Industry Guide -Number 2 -Paragraph 5 + Details
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- Definition The cash outflow to purchase long lived physical asset for use in the normal oil and gas operations and to purchase mineral interests in oil and gas properties not intended for resale. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Investing Activities -URI http://asc.fasb.org/extlink&oid=6516133 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 13 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3213-108585 + Details
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