Annual report pursuant to Section 13 and 15(d)

Acquisitions (Details)

v2.4.1.9
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                                             $ 10,000,000us-gaap_EscrowDeposit    
Proceeds from issuance of common stock, net of offering costs                   689,000us-gaap_ProceedsFromIssuanceOfCommonStock 766,495,000us-gaap_ProceedsFromIssuanceOfCommonStock 427,091,000us-gaap_ProceedsFromIssuanceOfCommonStock                          
Net revenues   267,697,000us-gaap_Revenues 170,804,000us-gaap_Revenues 114,736,000us-gaap_Revenues 118,029,000us-gaap_Revenues 68,067,000us-gaap_Revenues 69,252,000us-gaap_Revenues 70,434,000us-gaap_Revenues 55,000,000us-gaap_Revenues 671,266,000us-gaap_Revenues 262,753,000us-gaap_Revenues 248,926,000us-gaap_Revenues                          
Lease operating expenses                   52,191,000us-gaap_LeaseOperatingExpense 26,703,000us-gaap_LeaseOperatingExpense 24,308,000us-gaap_LeaseOperatingExpense                          
Common Stock [Member] | Public Offering [Member]                                                  
Business Acquisition [Line Items]                                                  
Stock option, portion attributable to underwriters (shares)                             900,000gpor_StockIssuedDuringPeriodSharesOverAllotmentOptionPortionAttributableToUnderwriters
/ gpor_SaleOfStockAxis
= gpor_PublicOfferingMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonStockMember
750,000gpor_StockIssuedDuringPeriodSharesOverAllotmentOptionPortionAttributableToUnderwriters
/ gpor_SaleOfStockAxis
= gpor_PublicOfferingMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonStockMember
                 
Proceeds from issuance of common stock, net of offering costs                         408,000,000us-gaap_ProceedsFromIssuanceOfCommonStock
/ gpor_SaleOfStockAxis
= gpor_PublicOfferingMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonStockMember
325,800,000us-gaap_ProceedsFromIssuanceOfCommonStock
/ gpor_SaleOfStockAxis
= gpor_PublicOfferingMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonStockMember
  460,700,000us-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                           22,000us-gaap_GasAndOilAreaUndevelopedNet
/ us-gaap_BusinessAcquisitionAxis
= gpor_UticaShaleMember
  37,000us-gaap_GasAndOilAreaUndevelopedNet
/ us-gaap_BusinessAcquisitionAxis
= gpor_UticaShaleMember
      7,000us-gaap_GasAndOilAreaUndevelopedNet
/ us-gaap_BusinessAcquisitionAxis
= gpor_UticaShaleMember
37,000us-gaap_GasAndOilAreaUndevelopedNet
/ us-gaap_BusinessAcquisitionAxis
= gpor_UticaShaleMember
    8,000us-gaap_GasAndOilAreaUndevelopedNet
/ us-gaap_BusinessAcquisitionAxis
= gpor_UticaShaleMember
30,000us-gaap_GasAndOilAreaUndevelopedNet
/ us-gaap_BusinessAcquisitionAxis
= gpor_UticaShaleMember
Cash price of ownership interest                           220,000,000us-gaap_PaymentsToAcquireOilAndGasPropertyAndEquipment
/ us-gaap_BusinessAcquisitionAxis
= gpor_UticaShaleMember
      70,000,000us-gaap_PaymentsToAcquireOilAndGasPropertyAndEquipment
/ us-gaap_BusinessAcquisitionAxis
= gpor_UticaShaleMember
302,000,000us-gaap_PaymentsToAcquireOilAndGasPropertyAndEquipment
/ us-gaap_BusinessAcquisitionAxis
= gpor_UticaShaleMember
372,000,000us-gaap_PaymentsToAcquireOilAndGasPropertyAndEquipment
/ us-gaap_BusinessAcquisitionAxis
= gpor_UticaShaleMember
         
Amount put in escrow                           33,600,000us-gaap_EscrowDeposit
/ us-gaap_BusinessAcquisitionAxis
= gpor_UticaShaleMember
  53,900,000us-gaap_EscrowDeposit
/ us-gaap_BusinessAcquisitionAxis
= gpor_UticaShaleMember
        53,900,000us-gaap_EscrowDeposit
/ us-gaap_BusinessAcquisitionAxis
= gpor_UticaShaleMember
       
Proceeds from issuance of common stock, net of offering costs                           325,800,000us-gaap_ProceedsFromIssuanceOfCommonStock
/ us-gaap_BusinessAcquisitionAxis
= gpor_UticaShaleMember
            460,700,000us-gaap_ProceedsFromIssuanceOfCommonStock
/ us-gaap_BusinessAcquisitionAxis
= gpor_UticaShaleMember
       
Existing wells excluded                           14gpor_NumberOfWellsOwned
/ us-gaap_BusinessAcquisitionAxis
= gpor_UticaShaleMember
                     
Future wells excluded                           16gpor_NumberOfProposedFutureWellsExcludedFromAcquisition
/ us-gaap_BusinessAcquisitionAxis
= gpor_UticaShaleMember
                     
Purchase price                   182,000,000us-gaap_BusinessCombinationConsiderationTransferred1
/ us-gaap_BusinessAcquisitionAxis
= gpor_UticaShaleMember
                             
Cash, net of purchase price adjustments                   179,500,000gpor_PaymenttoAcquireOilandGasPropertyandEquipmentNet
/ us-gaap_BusinessAcquisitionAxis
= gpor_UticaShaleMember
            179,527,000gpor_PaymenttoAcquireOilandGasPropertyandEquipmentNet
/ us-gaap_BusinessAcquisitionAxis
= gpor_UticaShaleMember
               
Net revenues                                           6,400,000us-gaap_Revenues
/ us-gaap_BusinessAcquisitionAxis
= gpor_UticaShaleMember
     
Lease operating expenses                                           $ 1,000,000us-gaap_LeaseOperatingExpense
/ us-gaap_BusinessAcquisitionAxis
= gpor_UticaShaleMember