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Investments - Additional Information (Detail) (USD $)
Dec. 31, 2014
Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]    
Gross unrealized losses $ 6,899,000us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss $ 7,578,000us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
Gross unrealized losses 12 months or greater 1,739,000us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss [1] 260,000us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss [1]
Investments in insurance enhanced municipal bonds 16,406,000gbli_InvestmentInInsuranceEnhancedMunicipalBonds  
Ratings without insurance 1,251,000gbli_MunicipalBondsRatingsWithoutInsurance  
Investments in asset backed and taxable municipal bonds 19,400,000gbli_InvestmentInAssetBackedAndTaxableMunicipalBonds  
Asset backed and taxable municipal bonds as a percentage of total cash and invested assets 1.30%gbli_AssetBackedAndTaxableMunicipalBondsAsPercentageOfCashAndInvestedAssets  
AA- Rating    
Schedule of Available-for-sale Securities [Line Items]    
Investments in insurance enhanced asset backed and credit securities 35,800,000gbli_InvestmentInInsuranceEnhancedAssetBackAndCreditSecurities
/ invest_CreditRatingSourceAxis
= gbli_AverageAAMinusRatingsMember		  
Investments in insurance enhanced municipal bonds 16,400,000gbli_InvestmentInInsuranceEnhancedMunicipalBonds
/ invest_CreditRatingSourceAxis
= gbli_AverageAAMinusRatingsMember		  
Insurance enhanced municipal bonds as a percentage of total cash and invested assets 1.10%gbli_InsuranceEnhancedMunicipalBondsAsPercentageOfCashAndInvestedAssets
/ invest_CreditRatingSourceAxis
= gbli_AverageAAMinusRatingsMember		  
Insurance enhanced municipal bonds 10,300,000gbli_InsuranceEnhancedMunicipalBondsNotPrerefunded
/ invest_CreditRatingSourceAxis
= gbli_AverageAAMinusRatingsMember		  
Maximum    
Schedule of Available-for-sale Securities [Line Items]    
Investments in a single issuer as a percentage of shareholders' equity 4.00%gbli_InvestmentsInSingleIssuerAsPercentageOfShareholdersEquity
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		 4.00%gbli_InvestmentsInSingleIssuerAsPercentageOfShareholdersEquity
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
Financial Guarantors    
Schedule of Available-for-sale Securities [Line Items]    
Investments in insurance enhanced municipal bonds 10,480,000gbli_InvestmentInInsuranceEnhancedMunicipalBonds
/ us-gaap_InvestmentTypeAxis
= gbli_FinancialGuarantorsMember		  
Pre-Refunded Securities    
Schedule of Available-for-sale Securities [Line Items]    
Investments in insurance enhanced municipal bonds 6,067,000gbli_InvestmentInInsuranceEnhancedMunicipalBonds
/ gbli_InsuranceEnhancedMuniBondsByFinancialGuarantorsAxis
= gbli_PreRefundedSecuritiesMember		  
Pre-Refunded Securities | Financial Guarantors    
Schedule of Available-for-sale Securities [Line Items]    
Investments in insurance enhanced municipal bonds 141,000gbli_InvestmentInInsuranceEnhancedMunicipalBonds
/ gbli_InsuranceEnhancedMuniBondsByFinancialGuarantorsAxis
= gbli_PreRefundedSecuritiesMember
/ us-gaap_InvestmentTypeAxis
= gbli_FinancialGuarantorsMember		  
AA Rating    
Schedule of Available-for-sale Securities [Line Items]    
Ratings without insurance 1,251,000gbli_MunicipalBondsRatingsWithoutInsurance
/ us-gaap_CreditRatingStandardPoorsAxis
= us-gaap_StandardPoorsAARatingMember		  
Municipal Bond Insurance Association    
Schedule of Available-for-sale Securities [Line Items]    
Investments in asset backed and taxable municipal bonds 11,200,000gbli_InvestmentInAssetBackedAndTaxableMunicipalBonds
/ gbli_InsuranceEnhancedAxis
= gbli_MunicipalBondInsuranceAssociationMember		  
Ambac Financial Group    
Schedule of Available-for-sale Securities [Line Items]    
Investments in asset backed and taxable municipal bonds 1,000,000gbli_InvestmentInAssetBackedAndTaxableMunicipalBonds
/ gbli_InsuranceEnhancedAxis
= gbli_AmbacFinancialGroupMember		  
Assured Guaranty Corporation    
Schedule of Available-for-sale Securities [Line Items]    
Investments in asset backed and taxable municipal bonds 7,200,000gbli_InvestmentInAssetBackedAndTaxableMunicipalBonds
/ gbli_InsuranceEnhancedAxis
= gbli_AssuredGuarantyCorporationMember		  
Obligations of States and Political Subdivisions    
Schedule of Available-for-sale Securities [Line Items]    
Gross unrealized losses 697,000us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		  
Obligations of States and Political Subdivisions | A- Rating    
Schedule of Available-for-sale Securities [Line Items]    
Gross unrealized losses 12 months or greater 383,000us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_CreditRatingStandardPoorsAxis
= us-gaap_StandardPoorsAMinusRatingMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		  
Common Shares    
Schedule of Available-for-sale Securities [Line Items]    
Gross unrealized losses 2,938,000us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommonStockMember		 636,000us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommonStockMember
Gross unrealized losses 12 months or greater 130,000us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommonStockMember		 [1] 9,000us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommonStockMember		 [1]
U.S. Treasury and Agency Obligations    
Schedule of Available-for-sale Securities [Line Items]    
Gross unrealized losses 83,000us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember		  
U.S. Treasury and Agency Obligations | AA+ Rating    
Schedule of Available-for-sale Securities [Line Items]    
Gross unrealized losses 12 months or greater 74,000us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_CreditRatingStandardPoorsAxis
= us-gaap_StandardPoorsAAPlusRatingMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember		  
Mortgage Backed Securities    
Schedule of Available-for-sale Securities [Line Items]    
Gross unrealized losses 764,000us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesMember		  
Mortgage Backed Securities | AA+ Rating    
Schedule of Available-for-sale Securities [Line Items]    
Gross unrealized losses 12 months or greater 757,000us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_CreditRatingStandardPoorsAxis
= us-gaap_StandardPoorsAAPlusRatingMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesMember		  
Asset-backed Securities    
Schedule of Available-for-sale Securities [Line Items]    
Gross unrealized losses 303,000us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember		  
Weighted average credit enhancement 20.50%gbli_WeightedAverageCreditEnhancementOfPortfolioPercentage
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember		  
Asset-backed Securities | A Rating    
Schedule of Available-for-sale Securities [Line Items]    
Gross unrealized losses 12 months or greater 20,000us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_CreditRatingStandardPoorsAxis
= us-gaap_StandardPoorsARatingMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember		  
Commercial Mortgage-Backed Securities    
Schedule of Available-for-sale Securities [Line Items]    
Gross unrealized losses 847,000us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember		  
Weighted average credit enhancement 33.50%gbli_WeightedAverageCreditEnhancementOfPortfolioPercentage
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember		  
Commercial Mortgage-Backed Securities | AA Rating    
Schedule of Available-for-sale Securities [Line Items]    
Gross unrealized losses 12 months or greater 322,000us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_CreditRatingStandardPoorsAxis
= us-gaap_StandardPoorsAARatingMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember		  
Corporate bonds and loans    
Schedule of Available-for-sale Securities [Line Items]    
Gross unrealized losses 709,000us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		  
Corporate bonds and loans | A+ Rating    
Schedule of Available-for-sale Securities [Line Items]    
Gross unrealized losses 12 months or greater 53,000us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_CreditRatingStandardPoorsAxis
= us-gaap_StandardPoorsAPlusRatingMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		  
Foreign Corporate Bonds    
Schedule of Available-for-sale Securities [Line Items]    
Gross unrealized losses $ 558,000us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ForeignCorporateDebtSecuritiesMember		  
Percentage of securities in unrealized loss position for twelve months or longer and rated investment grade 96.20%gbli_PercentageOfSecuritiesInUnrealizedLossPositionForTwelveMonthsOrLongerAndRatedInvestmentGrade
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ForeignCorporateDebtSecuritiesMember		  
[1] Fixed maturities in a gross unrealized loss position for twelve months or longer are primarily comprised of non-credit losses on investment grade securities where management does not intend to sell, and it is more likely than not that the Company will not be forced to sell the security before recovery. The Company has analyzed these securities and has determined that they are not other than temporarily impaired.