INCOME TAXES - CARES ACT IMPACT (Details)	12 Months Ended
Dec. 31, 2021 USD ($)
C A R E S Act Impact [Abstract]
Employee retention credit, CARES Act	$ 1,152,000

Carrying amount as of the balance sheet date of employer taxes paid to tax authorities representing refunds based on calculated eligible credits. Also called employer tax refund receivable.

No definition available.

Name:	gern_EmployerTaxReceivable
Namespace Prefix:	gern_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration