Number of severance plan.

No definition available.

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

- Definition

Purchase Obligation, Written Notice Term

+ References

No definition available.

+ Details

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

- References

No definition available.

+ Details

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

- Definition

The minimum amount the entity agreed to spend under the long-term purchase commitment.

+ References

No definition available.

+ Details

Name:	us-gaap_LongTermPurchaseCommitmentAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The total number of new claims filed pertaining to a loss contingency during the period.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 450
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483076/450-20-50-4

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 450
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 9
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483076/450-20-50-9

+ Details

Name:	us-gaap_LossContingencyNewClaimsFiledNumber
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of the recorded obligation to transfer funds in the future for fixed or minimum amounts or quantities of goods or services at fixed or minimum prices (for example, as in take-or-pay contracts or throughput contracts).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 440
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482648/440-10-50-6

+ Details

Name:	us-gaap_RecordedUnconditionalPurchaseObligation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The number of positions eliminated during the period as a percentage of total positions eliminated during the period in connection with the restructuring plan(s).

+ References

No definition available.

+ Details

Name:	us-gaap_RestructuringAndRelatedCostNumberOfPositionsEliminatedPeriodPercent
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

COMMITMENTS AND CONTINGENCIES (Details) $ in Millions					1 Months Ended		3 Months Ended
COMMITMENTS AND CONTINGENCIES (Details) $ in Millions	Aug. 29, 2025 action	May 16, 2025 lawsuit	Apr. 16, 2025 lawsuit	Mar. 14, 2025 lawsuit	Feb. 19, 2026 action	Dec. 31, 2025	Mar. 31, 2026 USD ($) plan
Commitments and Contingencies Disclosure [Abstract]
Number of putative securities lawsuits	1	1	3	2	2
Number of severance plan \| plan							2
Restructuring and related cost, number of positions eliminated, period percent						33.33%
Noncancelable commercial purchase commitments							$ 15.9
Long-term manufacturing commitments, amount							$ 37.7
Purchase obligation, written notice term							180 days