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Contingencies (Details) (USD $) | 12 Months Ended
--- | ---
Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2011
Loss Contingencies [Line Items] |  |  |  |
Cash, Uninsured Amount | 140,900,000 us-gaap_CashUninsuredAmount |  |  |
Maximum [Member] |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Cash, FDIC Insured Amount | 250,000 us-gaap_CashFDICInsuredAmount / us-gaap_RangeAxis = us-gaap_MaximumMember |  |  |
Shell Trading Company [Member] | Oil [Member] |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Percentage Of Production Sold | 99.00%gpor_PercentageOfProductionSold / us-gaap_AverageSalesPriceAndProductionCostsPerUnitOfProductionProductionTypeAxis = us-gaap_OilReservesMember / us-gaap_MajorCustomersAxis = gpor_ShellTradingCompanyMember | 99.00%gpor_PercentageOfProductionSold / us-gaap_AverageSalesPriceAndProductionCostsPerUnitOfProductionProductionTypeAxis = us-gaap_OilReservesMember / us-gaap_MajorCustomersAxis = gpor_ShellTradingCompanyMember | 92.00%gpor_PercentageOfProductionSold / us-gaap_AverageSalesPriceAndProductionCostsPerUnitOfProductionProductionTypeAxis = us-gaap_OilReservesMember / us-gaap_MajorCustomersAxis = gpor_ShellTradingCompanyMember |
Markwest Utica [Member] | Natural Gas Liquids [Member] |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Percentage Of Production Sold | 100.00%gpor_PercentageOfProductionSold / us-gaap_AverageSalesPriceAndProductionCostsPerUnitOfProductionProductionTypeAxis = us-gaap_NaturalGasLiquidsReservesMember / us-gaap_MajorCustomersAxis = gpor_MarkwestUticaMember | 100.00%gpor_PercentageOfProductionSold / us-gaap_AverageSalesPriceAndProductionCostsPerUnitOfProductionProductionTypeAxis = us-gaap_NaturalGasLiquidsReservesMember / us-gaap_MajorCustomersAxis = gpor_MarkwestUticaMember |  |
Sequent [Member] | Natural Gas, Per Thousand Cubic Feet [Member] |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Percentage Of Production Sold | 32.00%gpor_PercentageOfProductionSold / us-gaap_AverageSalesPriceAndProductionCostsPerUnitOfProductionProductionTypeAxis = us-gaap_NaturalGasPerThousandCubicFeetMember / us-gaap_MajorCustomersAxis = gpor_SequentMember |  |  |
Diamondback [Member] | Oil [Member] |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Percentage Of Production Sold |  |  | 8.00%gpor_PercentageOfProductionSold / us-gaap_AverageSalesPriceAndProductionCostsPerUnitOfProductionProductionTypeAxis = us-gaap_OilReservesMember / us-gaap_MajorCustomersAxis = gpor_DiamondbackMember |
Diamondback [Member] | Natural Gas Liquids [Member] |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Percentage Of Production Sold |  |  | 91.00%gpor_PercentageOfProductionSold / us-gaap_AverageSalesPriceAndProductionCostsPerUnitOfProductionProductionTypeAxis = us-gaap_NaturalGasLiquidsReservesMember / us-gaap_MajorCustomersAxis = gpor_DiamondbackMember |
Noble Americas Gas [Member] | Natural Gas, Per Thousand Cubic Feet [Member] |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Percentage Of Production Sold |  |  |  | 41.00%gpor_PercentageOfProductionSold / us-gaap_AverageSalesPriceAndProductionCostsPerUnitOfProductionProductionTypeAxis = us-gaap_NaturalGasPerThousandCubicFeetMember / us-gaap_MajorCustomersAxis = gpor_NobleAmericasGasMember
North American Gas [Member] | Natural Gas, Per Thousand Cubic Feet [Member] |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Percentage Of Production Sold |  | 32.00%gpor_PercentageOfProductionSold / us-gaap_AverageSalesPriceAndProductionCostsPerUnitOfProductionProductionTypeAxis = us-gaap_NaturalGasPerThousandCubicFeetMember / us-gaap_MajorCustomersAxis = gpor_NorthAmericanGasMember |  |
Hess [Member] | Natural Gas, Per Thousand Cubic Feet [Member] |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Percentage Of Production Sold | 19.00%gpor_PercentageOfProductionSold / us-gaap_AverageSalesPriceAndProductionCostsPerUnitOfProductionProductionTypeAxis = us-gaap_NaturalGasPerThousandCubicFeetMember / us-gaap_MajorCustomersAxis = gpor_HessMember | 31.00%gpor_PercentageOfProductionSold / us-gaap_AverageSalesPriceAndProductionCostsPerUnitOfProductionProductionTypeAxis = us-gaap_NaturalGasPerThousandCubicFeetMember / us-gaap_MajorCustomersAxis = gpor_HessMember |  | 18.00%gpor_PercentageOfProductionSold / us-gaap_AverageSalesPriceAndProductionCostsPerUnitOfProductionProductionTypeAxis = us-gaap_NaturalGasPerThousandCubicFeetMember / us-gaap_MajorCustomersAxis = gpor_HessMember
Interstate Gas [Member] | Natural Gas, Per Thousand Cubic Feet [Member] |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Percentage Of Production Sold | 40.00%gpor_PercentageOfProductionSold / us-gaap_AverageSalesPriceAndProductionCostsPerUnitOfProductionProductionTypeAxis = us-gaap_NaturalGasPerThousandCubicFeetMember / us-gaap_MajorCustomersAxis = gpor_InterstateGasMember | 17.00%gpor_PercentageOfProductionSold / us-gaap_AverageSalesPriceAndProductionCostsPerUnitOfProductionProductionTypeAxis = us-gaap_NaturalGasPerThousandCubicFeetMember / us-gaap_MajorCustomersAxis = gpor_InterstateGasMember |  |
Chevron [Member] | Natural Gas, Per Thousand Cubic Feet [Member] |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Percentage Of Production Sold |  |  |  | 16.00%gpor_PercentageOfProductionSold / us-gaap_AverageSalesPriceAndProductionCostsPerUnitOfProductionProductionTypeAxis = us-gaap_NaturalGasPerThousandCubicFeetMember / us-gaap_MajorCustomersAxis = gpor_ChevronMember

X
- Definition Percentage of production sold to purchaser in the period + References No definition available. + Details
Name: | gpor_PercentageOfProductionSold
Namespace Prefix: | gpor_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition The amount of cash deposited in financial institutions as of the balance sheet date that is insured by the Federal Deposit Insurance Corporation. + References No definition available. + Details
Name: | us-gaap_CashFDICInsuredAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The amount of cash as of the balance sheet date that is not insured by the Federal Deposit Insurance Corporation. + References No definition available. + Details
Name: | us-gaap_CashUninsuredAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_LossContingenciesLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_MajorCustomersAxis=gpor_ChevronMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorCustomersAxis=gpor_DiamondbackMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorCustomersAxis=gpor_HessMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorCustomersAxis=gpor_InterstateGasMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorCustomersAxis=gpor_MarkwestUticaMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorCustomersAxis=gpor_NobleAmericasGasMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorCustomersAxis=gpor_NorthAmericanGasMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorCustomersAxis=gpor_SequentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorCustomersAxis=gpor_ShellTradingCompanyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |