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ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details 5) (Concentrations of Customers and Suppliers)	12 Months Ended
	Dec. 31, 2014 item	Dec. 31, 2013 item	Dec. 31, 2012 item
Concentrations of Customers and Suppliers
Concentration risk
Number of customers	2gern_NumberOfCustomers / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember	2gern_NumberOfCustomers / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember	2gern_NumberOfCustomers / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember
Concentration risk percentage	31.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember	42.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember	59.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember

X

- Definition

Represents the number of customers that accounted for the majority of the entity's revenues during the period.

+ References

No definition available.

+ Details

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

X

- Details

Name:	us-gaap_ConcentrationRiskLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
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Period Type:	duration

X

- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 21

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13537-108611



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 275

-SubTopic 10

-Section 50

-Paragraph 20

-URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6404-108592



Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 20

-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13531-108611



Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 275

-SubTopic 10

-Section 50

-Paragraph 18

-URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6351-108592

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration