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Derivative instruments (Details) - Commodity futures | 9 Months Ended
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Sep. 30, 2022
Minimum |
Derivative instruments |
Percentage of hedging | 50.00%
Expected hedging term | 12 months
Maximum |
Derivative instruments |
Percentage of hedging | 75.00%
Expected hedging term | 24 months

X
- Definition Hedging term of expected oil and gas production. + References No definition available. + Details
Name: | grnt_HedgingTermOfExpectedOilAndGasProduction
Namespace Prefix: | grnt_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage of hedging. + References No definition available. + Details
Name: | grnt_PercentageOfHedging
Namespace Prefix: | grnt_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- 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
Name: | us-gaap_DerivativeLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | srt_RangeAxis=srt_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DerivativeInstrumentRiskAxis=us-gaap_CommodityContractMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |