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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

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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- Definition

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

+ References

No definition available.

+ Details

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