Quarterly report pursuant to Section 13 or 15(d)

Hedging Activities (Schedule Of Derivative Instruments) (Details)

v2.4.1.9
Hedging Activities (Schedule Of Derivative Instruments) (Details)
Mar. 31, 2015
Fixed Price Swap, April 2015 through June 2016 [Member]  
Derivative [Line Items]  
Daily Volume 1,000invest_DerivativeNonmonetaryNotionalAmount
/ us-gaap_DerivativeByNatureAxis
= gpor_FixedPriceSwapApril2015throughJune2016Member
Weighted Average Price 62.25us-gaap_DerivativeSwapTypeAverageFixedPrice
/ us-gaap_DerivativeByNatureAxis
= gpor_FixedPriceSwapApril2015throughJune2016Member
Fixed Price Swap, April 2015 [Member]  
Derivative [Line Items]  
Daily Volume 191,250invest_DerivativeNonmonetaryNotionalAmount
/ us-gaap_DerivativeByNatureAxis
= gpor_FuelPriceSwapApril2015Member
Weighted Average Price 4.05us-gaap_DerivativeSwapTypeAverageFixedPrice
/ us-gaap_DerivativeByNatureAxis
= gpor_FuelPriceSwapApril2015Member
Fixed Price Swap, May through June 2015 [Member]  
Derivative [Line Items]  
Daily Volume 201,250invest_DerivativeNonmonetaryNotionalAmount
/ us-gaap_DerivativeByNatureAxis
= gpor_FixedPriceSwapMaythroughJune2015Member
Weighted Average Price 4.05us-gaap_DerivativeSwapTypeAverageFixedPrice
/ us-gaap_DerivativeByNatureAxis
= gpor_FixedPriceSwapMaythroughJune2015Member
Fixed Price Swap, July through August 2015 [Member]  
Derivative [Line Items]  
Daily Volume 216,875invest_DerivativeNonmonetaryNotionalAmount
/ us-gaap_DerivativeByNatureAxis
= gpor_FixedPriceSwapJulythroughAugust2015Member
Weighted Average Price 4.04us-gaap_DerivativeSwapTypeAverageFixedPrice
/ us-gaap_DerivativeByNatureAxis
= gpor_FixedPriceSwapJulythroughAugust2015Member
Fixed Price Swap, September 2015 [Member]  
Derivative [Line Items]  
Daily Volume 246,875invest_DerivativeNonmonetaryNotionalAmount
/ us-gaap_DerivativeByNatureAxis
= gpor_FixedPriceSwapSeptember2015Member
Weighted Average Price 3.97us-gaap_DerivativeSwapTypeAverageFixedPrice
/ us-gaap_DerivativeByNatureAxis
= gpor_FixedPriceSwapSeptember2015Member
Fixed Price Swap, October through December 2015 [Member]  
Derivative [Line Items]  
Daily Volume 262,500invest_DerivativeNonmonetaryNotionalAmount
/ us-gaap_DerivativeByNatureAxis
= gpor_FixedPriceSwapOctoberthroughDecember2015Member
Weighted Average Price 3.96us-gaap_DerivativeSwapTypeAverageFixedPrice
/ us-gaap_DerivativeByNatureAxis
= gpor_FixedPriceSwapOctoberthroughDecember2015Member
Fixed Price Swap, January through March 2016 [Member]  
Derivative [Line Items]  
Daily Volume 252,500invest_DerivativeNonmonetaryNotionalAmount
/ us-gaap_DerivativeByNatureAxis
= gpor_FixedPriceSwapJanuarythroughMarch2016Member
Weighted Average Price 3.82us-gaap_DerivativeSwapTypeAverageFixedPrice
/ us-gaap_DerivativeByNatureAxis
= gpor_FixedPriceSwapJanuarythroughMarch2016Member
Fixed Price Swap, April 2016 [Member]  
Derivative [Line Items]  
Daily Volume 242,500invest_DerivativeNonmonetaryNotionalAmount
/ us-gaap_DerivativeByNatureAxis
= gpor_FixedPriceSwapApril2016Member
Weighted Average Price 3.81us-gaap_DerivativeSwapTypeAverageFixedPrice
/ us-gaap_DerivativeByNatureAxis
= gpor_FixedPriceSwapApril2016Member
Fixed Price Swap, May through December 2016 [Member]  
Derivative [Line Items]  
Daily Volume 172,500invest_DerivativeNonmonetaryNotionalAmount
/ us-gaap_DerivativeByNatureAxis
= gpor_FuelPriceSwapMaythroughDecember2016Member
Weighted Average Price 3.73us-gaap_DerivativeSwapTypeAverageFixedPrice
/ us-gaap_DerivativeByNatureAxis
= gpor_FuelPriceSwapMaythroughDecember2016Member
Fixed Price Swap, January through June 2017 [Member]  
Derivative [Line Items]  
Daily Volume 142,500invest_DerivativeNonmonetaryNotionalAmount
/ us-gaap_DerivativeByNatureAxis
= gpor_FixedPriceSwapJanuarythroughJune2017Member
Weighted Average Price 3.67us-gaap_DerivativeSwapTypeAverageFixedPrice
/ us-gaap_DerivativeByNatureAxis
= gpor_FixedPriceSwapJanuarythroughJune2017Member
Fixed Price Swap, July through December 2017 [Member]  
Derivative [Line Items]  
Daily Volume 80,000invest_DerivativeNonmonetaryNotionalAmount
/ us-gaap_DerivativeByNatureAxis
= gpor_FixedPriceSwapJulythroughDecember2017Member
Weighted Average Price 3.45us-gaap_DerivativeSwapTypeAverageFixedPrice
/ us-gaap_DerivativeByNatureAxis
= gpor_FixedPriceSwapJulythroughDecember2017Member
Fixed Price Swap, January through December 2018 [Member]  
Derivative [Line Items]  
Daily Volume 30,000invest_DerivativeNonmonetaryNotionalAmount
/ us-gaap_DerivativeByNatureAxis
= gpor_FixedPriceSwapJanuarythroughDecember2018Member
Weighted Average Price 3.40us-gaap_DerivativeSwapTypeAverageFixedPrice
/ us-gaap_DerivativeByNatureAxis
= gpor_FixedPriceSwapJanuarythroughDecember2018Member
Fixed Price Swap, April 2015 through December 2016, Option One [Member]  
Derivative [Line Items]  
Daily Volume 30,000invest_DerivativeNonmonetaryNotionalAmount
/ us-gaap_DerivativeByNatureAxis
= gpor_FixedPriceSwapApril2015throughDecember2016OptionOneMember
Weighted Average Price 0.02us-gaap_DerivativeSwapTypeAverageFixedPrice
/ us-gaap_DerivativeByNatureAxis
= gpor_FixedPriceSwapApril2015throughDecember2016OptionOneMember
Fixed Price Swap, April 2015 through December 2016, Option Two [Member]  
Derivative [Line Items]  
Daily Volume 10,000invest_DerivativeNonmonetaryNotionalAmount
/ us-gaap_DerivativeByNatureAxis
= gpor_FixedPriceSwapApril2015throughDecember2016OptionTwoMember
Weighted Average Price 0.01us-gaap_DerivativeSwapTypeAverageFixedPrice
/ us-gaap_DerivativeByNatureAxis
= gpor_FixedPriceSwapApril2015throughDecember2016OptionTwoMember