License Agreements and Collaborations (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended	3 Months Ended	9 Months Ended
Mar. 30, 2012	Aug. 31, 2011	Sep. 30, 2012	Sep. 30, 2012
License Agreements and Collaborations Collaborations (Textual) [Abstract]
Upfront development payment to the company	$ 9.0	$ 3.0
Funding of development costs	0.8	1.5
Potential for an additional payment	3.0	3.0
Option terminates days				60 days
Revenue recognized under the First Total			0.4	1.7
Revenue recognized under the Second Total			2.9	3.3
Deferred revenue First			1.6	1.6
Deferred revenue Second			$ 6.0	$ 6.0

Deferred revenue under first development program.

No definition available.

Name:	geva_DeferredRevenueUnderFirstDevelopmentProgram
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Deferred revenue under second development program.

No definition available.

Name:	geva_DeferredRevenueUnderSecondDevelopmentProgram
Namespace Prefix:	geva_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Development costs funding during initial development period.

No definition available.

Name:	geva_DevelopmentCostsFundingDuringInitialDevelopmentPeriod
Namespace Prefix:	geva_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Option for royalty bearing license obtainment expiration period.

No definition available.

Name:	geva_OptionForRoyaltyBearingLicenseObtainmentExpirationPeriod
Namespace Prefix:	geva_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Potential payment of development costs upon completion of initial development.

No definition available.

Name:	geva_PotentialPaymentOfDevelopmentCostsUponCompletionOfInitialDevelopment
Namespace Prefix:	geva_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Revenue recognition development programs revenue recognized under first development program.

No definition available.

Name:	geva_RevenueRecognitionDevelopmentProgramsRevenueRecognizedUnderFirstDevelopmentProgram
Namespace Prefix:	geva_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Revenue recognition development programs revenue recognized under second development program.

No definition available.

Name:	geva_RevenueRecognitionDevelopmentProgramsRevenueRecognizedUnderSecondDevelopmentProgram
Namespace Prefix:	geva_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Upfront development payment to the company.

No definition available.

Name:	geva_UpfrontDevelopmentPaymentToCompany
Namespace Prefix:	geva_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration