Name:	gern_ShareBasedCompensationArrangementByShareBasedPaymentAwardDurationOfNewOfferingPeriod
Namespace Prefix:	gern_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Represents the duration of the purchase period under the employee stock purchase plan.

No definition available.

Name:	gern_ShareBasedCompensationArrangementByShareBasedPaymentAwardDurationOfPurchasePeriod
Namespace Prefix:	gern_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Represents the maximum duration of the offering period under the employee stock purchase plan.

No definition available.

Name:	gern_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumDurationOfOfferingPeriod
Namespace Prefix:	gern_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Represents the number of offering periods in which an employee can participate at a time in the purchase plan.

No definition available.

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

Represents the maximum percentage of annual salary that an employee can choose to have withheld to purchase common stock under the purchase plan.

No definition available.

Name:	gern_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumPercentageOfAnnualSalaryThatCanBeWithheld
Namespace Prefix:	gern_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Represents the number of consecutive purchase periods in an offering period in the purchase plan.

No definition available.

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

Represents the holding period from the date of purchase under the Purchase Plan before shares may be traded.

No definition available.

Name:	gern_ShareBasedCompensationArrangementByShareBasedPaymentAwardPeriodForWhichSharesMustBeHeldAfterPurchaseBeforeSharesMayBeTraded
Namespace Prefix:	gern_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Details

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

The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph a

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (a)(3)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

Purchase price of common stock expressed as a percentage of its fair market value.

No definition available.

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

Number of shares of stock issued as of the balance sheet date, including shares that had been issued and were previously outstanding but which are now held in the treasury.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644