XML 41 R30.htm IDEA: XBRL DOCUMENT
v3.25.3

FAIR VALUE MEASUREMENTS - Financial Instruments Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands | Sep. 30, 2025 | Dec. 31, 2024
--- | --- | ---
Fair Value on a Recurring Basis |  |
Marketable securities | $ 341,478 | $ 422,069
Recurring basis |  |
Fair Value on a Recurring Basis |  |
Assets | 378,581 | 474,121
Recurring basis | U.S. Treasury securities |  |
Fair Value on a Recurring Basis |  |
Marketable securities | 22,881 | 30,570
Recurring basis | Government-sponsored enterprise securities |  |
Fair Value on a Recurring Basis |  |
Marketable securities | 5,000 | 8,748
Recurring basis | Commercial paper |  |
Fair Value on a Recurring Basis |  |
Marketable securities | 123,238 | 185,201
Recurring basis | Corporate notes |  |
Fair Value on a Recurring Basis |  |
Marketable securities | 190,268 | 202,527
Recurring basis | Money market funds |  |
Fair Value on a Recurring Basis |  |
Cash, cash equivalents and restricted cash | 31,867 | 46,802
Recurring basis | Certificate of deposit |  |
Fair Value on a Recurring Basis |  |
Cash, cash equivalents and restricted cash | 274 | 273
Recurring basis | Municipal securities |  |
Fair Value on a Recurring Basis |  |
Cash, cash equivalents and restricted cash | 5,054 |
Recurring basis | Level 1 |  |
Fair Value on a Recurring Basis |  |
Assets | 32,140 | 47,075
Recurring basis | Level 1 | U.S. Treasury securities |  |
Fair Value on a Recurring Basis |  |
Marketable securities | 0 | 0
Recurring basis | Level 1 | Government-sponsored enterprise securities |  |
Fair Value on a Recurring Basis |  |
Marketable securities | 0 | 0
Recurring basis | Level 1 | Commercial paper |  |
Fair Value on a Recurring Basis |  |
Marketable securities | 0 | 0
Recurring basis | Level 1 | Corporate notes |  |
Fair Value on a Recurring Basis |  |
Marketable securities | 0 | 0
Recurring basis | Level 1 | Money market funds |  |
Fair Value on a Recurring Basis |  |
Cash, cash equivalents and restricted cash | 31,867 | 46,802
Recurring basis | Level 1 | Certificate of deposit |  |
Fair Value on a Recurring Basis |  |
Cash, cash equivalents and restricted cash | 274 | 273
Recurring basis | Level 1 | Municipal securities |  |
Fair Value on a Recurring Basis |  |
Cash, cash equivalents and restricted cash | 0 |
Recurring basis | Level 2 |  |
Fair Value on a Recurring Basis |  |
Assets | 346,441 | 427,046
Recurring basis | Level 2 | U.S. Treasury securities |  |
Fair Value on a Recurring Basis |  |
Marketable securities | 22,881 | 30,570
Recurring basis | Level 2 | Government-sponsored enterprise securities |  |
Fair Value on a Recurring Basis |  |
Marketable securities | 5,000 | 8,748
Recurring basis | Level 2 | Commercial paper |  |
Fair Value on a Recurring Basis |  |
Marketable securities | 123,238 | 185,201
Recurring basis | Level 2 | Corporate notes |  |
Fair Value on a Recurring Basis |  |
Marketable securities | 190,268 | 202,527
Recurring basis | Level 2 | Money market funds |  |
Fair Value on a Recurring Basis |  |
Cash, cash equivalents and restricted cash | 0 | 0
Recurring basis | Level 2 | Certificate of deposit |  |
Fair Value on a Recurring Basis |  |
Cash, cash equivalents and restricted cash | 0 | 0
Recurring basis | Level 2 | Municipal securities |  |
Fair Value on a Recurring Basis |  |
Cash, cash equivalents and restricted cash | 5,054 |
Recurring basis | Level 3 |  |
Fair Value on a Recurring Basis |  |
Assets | 0 | 0
Recurring basis | Level 3 | U.S. Treasury securities |  |
Fair Value on a Recurring Basis |  |
Marketable securities | 0 | 0
Recurring basis | Level 3 | Government-sponsored enterprise securities |  |
Fair Value on a Recurring Basis |  |
Marketable securities | 0 | 0
Recurring basis | Level 3 | Commercial paper |  |
Fair Value on a Recurring Basis |  |
Marketable securities | 0 | 0
Recurring basis | Level 3 | Corporate notes |  |
Fair Value on a Recurring Basis |  |
Marketable securities | 0 | 0
Recurring basis | Level 3 | Money market funds |  |
Fair Value on a Recurring Basis |  |
Cash, cash equivalents and restricted cash | 0 | 0
Recurring basis | Level 3 | Certificate of deposit |  |
Fair Value on a Recurring Basis |  |
Cash, cash equivalents and restricted cash | 0 | $ 0
Recurring basis | Level 3 | Municipal securities |  |
Fair Value on a Recurring Basis |  |
Cash, cash equivalents and restricted cash | $ 0 |

X
- Definition Cash And Cash Equivalents And Restricted Cash, Fair Value Disclosure + References No definition available. + Details
Name: | gern_CashAndCashEquivalentsAndRestrictedCashFairValueDisclosure
Namespace Prefix: | gern_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Fair value portion of asset recognized for present right to economic benefit. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 55 -Paragraph 100 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482078/820-10-55-100 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 + Details
Name: | us-gaap_AssetsFairValueDisclosure
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount excluding accrued interest, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 326 -SubTopic 30 -Name Accounting Standards Codification -Section 45 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479130/326-30-45-1 + Details
Name: | us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 55 -Paragraph 100 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482078/820-10-55-100 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-3 + Details
Name: | us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsRecurringMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_USTreasuryNotesSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_CommercialPaperMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_CorporateNoteSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_CashAndCashEquivalentsAxis=us-gaap_MoneyMarketFundsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_CashAndCashEquivalentsAxis=us-gaap_CertificatesOfDepositMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_CashAndCashEquivalentsAxis=us-gaap_MunicipalBondsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel1Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |