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Leases - Summary of Operating Leases (Details) - Copenhagen, Denmark | 6 Months Ended
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Jun. 30, 2025
Operating Leased Assets [Line Items] |
Operating lease, expiration date | Nov. 30, 2029
Operating lease,renewal option | None

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- Definition Date which lease or group of leases is set to expire, in YYYY-MM-DD format. + References No definition available. + Details
Name: | us-gaap_LeaseExpirationDate1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:dateItemType
Balance Type: | na
Period Type: | duration

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- Definition Description of terms and conditions of option to extend lessor's operating lease. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 842 -SubTopic 30 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (a)(3) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479773/842-30-50-3 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- 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 No definition available. + Details
Name: | us-gaap_OperatingLeasedAssetsLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | srt_StatementGeographicalAxis=glto_CopenhagenMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |