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FAIR VALUE MEASUREMENTS (Details 6)	12 Months Ended
	Dec. 31, 2014 item
Credit Risk
Number of financial institutions with which cash, restricted cash, cash equivalents and marketable securities are placed	4gern_NumberOfFinancialInstitutionsWithWhichCashCashEquivalentsAndMarketableSecuritiesArePlaced

X

- Definition

Represents the number of financial institutions with which cash, restricted cash, cash equivalents and marketable securities placed.

+ References

No definition available.

+ Details

Name:	gern_NumberOfFinancialInstitutionsWithWhichCashCashEquivalentsAndMarketableSecuritiesArePlaced
Namespace Prefix:	gern_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

X

- Details

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