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

Certain fees relating to the Company's business combination, which have been capitalized.

No definition available.

Name:	grnt_CapitalizedFeesBusinessCombination
Namespace Prefix:	grnt_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration