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v3.22.2.2

Summary of significant accounting policies - Other Assets (Details) - USD ($) | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2022 | Dec. 31, 2021
Summary of significant accounting policies |  |
Capitalized fees, business combination | $ 4,098,000 | $ 0
Prepaid expenses, business combination | $ 0 | $ 70,000

X
- Definition Certain fees relating to the Company's business combination, which have been capitalized. + References No definition available. + Details
Name: | grnt_CapitalizedFeesBusinessCombination
Namespace Prefix: | grnt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition prepaid expenses relating to the Company's business combination. + References No definition available. + Details
Name: | grnt_PrepaidExpensesBusinessCombination
Namespace Prefix: | grnt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_AccountingPoliciesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration