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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

X

- Definition

Aggregate notional amount of derivative expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 12

-Section 13

-Sentence Column B

+ Details

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- Details

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X

- Definition

Average fixed price related to the group of price risk swap derivatives.

+ References

No definition available.

+ Details

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