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Future Minimum Lease Payments Under Non-cancelable Operating Leases (Parenthetical) (Detail) $ in Millions | 12 Months Ended
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Dec. 31, 2022 USD ($)
Leases [Abstract] |
Impairment of leases on property no longer in use | $ 4.6

X
- Definition Impairment of leases on property no longer in use. + References No definition available. + Details
Name: | gbli_ImpairmentOfLeasesOnPropertyNoLongerInUse
Namespace Prefix: | gbli_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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