Annual report pursuant to Section 13 and 15(d)

Contingencies (Details)

v2.4.1.9
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 140,900,000us-gaap_CashUninsuredAmount      
Maximum [Member]        
Loss Contingencies [Line Items]        
Cash, FDIC Insured Amount 250,000us-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