Government Assistance - Additional Information (Detail) - COVID-19 Employee Retention Credit	12 Months Ended
Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($) Employees
Government Assistance [Line Items]
Government assistance recognized	$ 0	$ 5,500,000	$ 0
Government assistance amount received			$ 5,300,000
Government Assistance, Statement of Income or Comprehensive Income [Extensible Enumeration]	Other Cost and Expense, Operating	Other Cost and Expense, Operating	Other Cost and Expense, Operating
Percentage of qualified wages of employee			70.00%
Government assistance recognized per quarter			$ 7,000
Reduction to compensation cost		$ 5,300,000
Interest income		$ 200,000
Maximum
Government Assistance [Line Items]
Number of Persons Employed \| Employees			500

Number of persons employed by the Entity

No definition available.

Name:	dei_EntityNumberOfEmployees
Namespace Prefix:	dei_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

- Definition

Maximum credit per employee per quarter.

+ References

No definition available.

+ Details

Name:	gbli_MaximumCreditPerEmployeePerQuarter
Namespace Prefix:	gbli_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Percentage of qualified wages of employee.

+ References

No definition available.

+ Details

Name:	gbli_PercentageOfQualifiedWagesOfEmployee
Namespace Prefix:	gbli_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of government assistance credit that the Company qualified for.

+ References

No definition available.

+ Details

Name:	gbli_QualifiedGovernmentAssistanceCredit
Namespace Prefix:	gbli_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Reduction to compensation cost.

+ References

No definition available.

+ Details

Name:	gbli_ReductionToCompensationCost
Namespace Prefix:	gbli_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of government assistance recognized.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 832
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483507/832-10-50-3

+ Details

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

- 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

+ Details

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

- Definition

Indicates line item in statement of income or comprehensive income that includes government assistance.

+ References

+ Details

Name:	us-gaap_GovernmentAssistanceStatementOfIncomeOrComprehensiveIncomeExtensibleEnumeration
Namespace Prefix:	us-gaap_
Data Type:	enum2:enumerationSetItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of operating interest income, including, but not limited to, amortization and accretion of premiums and discounts on securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 320
-Name Accounting Standards Codification
-Section S99
-Paragraph 6
-Subparagraph (SX 210.12-14(Column E)(1))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480032/946-320-S99-6

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 320
-Name Accounting Standards Codification
-Section S99
-Paragraph 6
-Subparagraph (SX 210.12-14(Column E)(Footnote 4))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480032/946-320-S99-6

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Topic 946
-SubTopic 830
-Name Accounting Standards Codification
-Section 55
-Paragraph 10
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480167/946-830-55-10

Reference 4: http://www.xbrl.org/2003/role/exampleRef
-Topic 946
-SubTopic 830
-Name Accounting Standards Codification
-Section 45
-Paragraph 39
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480228/946-830-45-39

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(1)(b))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483575/946-220-S99-1

Reference 6: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 946
-SubTopic 320
-Name Accounting Standards Codification
-Section S99
-Paragraph 6
-Subparagraph (SX 210.12-14(Column E)(Footnote 6)(a))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480032/946-320-S99-6

Reference 7: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1(e))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483621/220-10-S99-2

+ Details

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

- Details

Name:	us-gaap_GovernmentAssistanceTypeAxis=gbli_CovidNineteenEmployeeRetentionCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: