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DERIVATIVE INSTRUMENTS (Narrative) (Details) $ in Millions | 1 Months Ended | 9 Months Ended
--- | --- | ---
Dec. 31, 2018 MMBTU $ / MMBTU | Sep. 30, 2019 USD ($)
Derivative [Line Items] |  |
Fair value of contingent consideration asset on date of divestiture | $ |  | $ 1.1
2019 |  |
Derivative [Line Items] |  |
Counterparty option to extend the original terms, number of months |  | 12 months
Daily volume (in MMBtu) | MMBTU | 100,000 |
Weighted average price (in usd per MMBtu or Bbl) | $ / MMBTU | 3.05 |

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- Definition Contingent Consideration Fair Value + References No definition available. + Details
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Namespace Prefix: | gpor_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Counterparty Option to Extend Original Terms, Number of Months + References No definition available. + Details
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Namespace Prefix: | gpor_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Nominal energy measure used to calculate payments on a derivative instrument. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | num:energyItemType
Balance Type: | na
Period Type: | duration

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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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Namespace Prefix: | us-gaap_
Data Type: | srt-types:perUnitItemType
Balance Type: | na
Period Type: | instant

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |