XML 50 R37.htm IDEA: XBRL DOCUMENT
v3.20.4

FAIR VALUE MEASUREMENTS - CREDIT RISK (Details) | Dec. 31, 2020 Institution
--- | ---
Credit Risk |
Number of financial institutions | 5

X
- Definition Number of financial institutions. + References No definition available. + Details
Name: | gern_NumberOfFinancialInstitutions
Namespace Prefix: | gern_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

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