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Income Tax (Details Textual)	Dec. 31, 2019 USD ($)
Income Tax Disclosure [Abstract]
Net operating loss carryovers	$ 14,652

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- Definition

Net operating loss carryovers.

+ References

No definition available.

+ Details

Name:	grnv_DeferredTaxAssetsOperatingLossCarryOvers
Namespace Prefix:	grnv_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

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- References

No definition available.

+ Details

Name:	us-gaap_IncomeTaxDisclosureAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration