Annual report pursuant to Section 13 and 15(d)

Hedging Activities (Schedule Of Derivative Instruments) (Details)

v2.4.1.9
Hedging Activities (Schedule Of Derivative Instruments) (Details)
Dec. 31, 2014
Fixed Price Swap, January 2014 [Member]  
Derivative [Line Items]  
Daily Volume 190,625invest_DerivativeNonmonetaryNotionalAmount
/ us-gaap_DerivativeByNatureAxis
= gpor_FixedPriceSwapJanuary2014Member
Weighted Average Price 4.12us-gaap_DerivativeSwapTypeAverageFixedPrice
/ us-gaap_DerivativeByNatureAxis
= gpor_FixedPriceSwapJanuary2014Member
Fixed Price Swap, February Though December 2014 [Member]  
Derivative [Line Items]  
Daily Volume 191,250invest_DerivativeNonmonetaryNotionalAmount
/ us-gaap_DerivativeByNatureAxis
= gpor_FixedPriceSwapFebruaryThoughDecember2014Member
Weighted Average Price 4.05us-gaap_DerivativeSwapTypeAverageFixedPrice
/ us-gaap_DerivativeByNatureAxis
= gpor_FixedPriceSwapFebruaryThoughDecember2014Member
Fixed Price Swap, May 2015 through June 2015 [Member]  
Derivative [Line Items]  
Daily Volume 201,250invest_DerivativeNonmonetaryNotionalAmount
/ us-gaap_DerivativeByNatureAxis
= gpor_FixedPriceSwapMay2015throughJune2015Member
Weighted Average Price 4.05us-gaap_DerivativeSwapTypeAverageFixedPrice
/ us-gaap_DerivativeByNatureAxis
= gpor_FixedPriceSwapMay2015throughJune2015Member
Fixed Price Swap, July 2015 through September 2015 [Member]  
Derivative [Line Items]  
Daily Volume 216,875invest_DerivativeNonmonetaryNotionalAmount
/ us-gaap_DerivativeByNatureAxis
= gpor_FixedPriceSwapJuly2015throughSeptember2015Member
Weighted Average Price 4.04us-gaap_DerivativeSwapTypeAverageFixedPrice
/ us-gaap_DerivativeByNatureAxis
= gpor_FixedPriceSwapJuly2015throughSeptember2015Member
Fixed Price Swap, January through December 2015 [Member]  
Derivative [Line Items]  
Daily Volume 232,500invest_DerivativeNonmonetaryNotionalAmount
/ us-gaap_DerivativeByNatureAxis
= gpor_FixedPriceSwapJanuarythroughDecember2015Member
Weighted Average Price 4.04us-gaap_DerivativeSwapTypeAverageFixedPrice
/ us-gaap_DerivativeByNatureAxis
= gpor_FixedPriceSwapJanuarythroughDecember2015Member
Fixed Price Swap, Period of January through March 2016 [Member]  
Derivative [Line Items]  
Daily Volume 172,500invest_DerivativeNonmonetaryNotionalAmount
/ us-gaap_DerivativeByNatureAxis
= gpor_FixedPriceSwapPeriodofJanuarythroughMarch2016Member
Weighted Average Price 3.99us-gaap_DerivativeSwapTypeAverageFixedPrice
/ us-gaap_DerivativeByNatureAxis
= gpor_FixedPriceSwapPeriodofJanuarythroughMarch2016Member
Fixed Price Swap, April 2016 [Member]  
Derivative [Line Items]  
Daily Volume 162,500invest_DerivativeNonmonetaryNotionalAmount
/ us-gaap_DerivativeByNatureAxis
= gpor_FixedPriceSwapApril2016Member
Weighted Average Price 3.99us-gaap_DerivativeSwapTypeAverageFixedPrice
/ us-gaap_DerivativeByNatureAxis
= gpor_FixedPriceSwapApril2016Member
Fixed Price Swap, May 2016 through December 2016 [Member]  
Derivative [Line Items]  
Daily Volume 92,500invest_DerivativeNonmonetaryNotionalAmount
/ us-gaap_DerivativeByNatureAxis
= gpor_FixedPriceSwapMay2016throughDecember2016Member
Weighted Average Price 3.97us-gaap_DerivativeSwapTypeAverageFixedPrice
/ us-gaap_DerivativeByNatureAxis
= gpor_FixedPriceSwapMay2016throughDecember2016Member
Fixed Price Swap, January 2017 through June 2017 [Member]  
Derivative [Line Items]  
Daily Volume 62,500invest_DerivativeNonmonetaryNotionalAmount
/ us-gaap_DerivativeByNatureAxis
= gpor_FixedPriceSwapJanuary2017throughJune2017Member
Weighted Average Price 3.96us-gaap_DerivativeSwapTypeAverageFixedPrice
/ us-gaap_DerivativeByNatureAxis
= gpor_FixedPriceSwapJanuary2017throughJune2017Member