wtm-20240331
000077686712/312024Q1falsexbrli:sharesiso4217:USDiso4217:USDxbrli:shareswtm:segmentxbrli:purewtm:fundiso4217:EURwtm:letterOfCreditwtm:credit_facilitywtm:contract00007768672024-01-012024-03-3100007768672024-05-060000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberus-gaap:OperatingSegmentsMember2024-03-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberus-gaap:OperatingSegmentsMember2023-12-310000776867wtm:HGGlobalBAMSegmentMemberus-gaap:OperatingSegmentsMember2024-03-310000776867wtm:HGGlobalBAMSegmentMemberus-gaap:OperatingSegmentsMember2023-12-310000776867wtm:KuduInvestmentManagementLLCSegmentMemberus-gaap:OperatingSegmentsMember2024-03-310000776867wtm:KuduInvestmentManagementLLCSegmentMemberus-gaap:OperatingSegmentsMember2023-12-310000776867wtm:BambooIde8InsuranceServicesLLCSegmentMemberus-gaap:OperatingSegmentsMember2024-03-310000776867wtm:BambooIde8InsuranceServicesLLCSegmentMemberus-gaap:OperatingSegmentsMember2023-12-310000776867us-gaap:CorporateNonSegmentMember2024-03-310000776867us-gaap:CorporateNonSegmentMember2023-12-3100007768672024-03-3100007768672023-12-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberus-gaap:OperatingSegmentsMember2024-01-012024-03-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberus-gaap:OperatingSegmentsMember2023-01-012023-03-310000776867wtm:HGGlobalBAMSegmentMemberus-gaap:OperatingSegmentsMember2024-01-012024-03-310000776867wtm:HGGlobalBAMSegmentMemberus-gaap:OperatingSegmentsMember2023-01-012023-03-310000776867wtm:KuduInvestmentManagementLLCSegmentMemberus-gaap:OperatingSegmentsMember2024-01-012024-03-310000776867wtm:KuduInvestmentManagementLLCSegmentMemberus-gaap:OperatingSegmentsMember2023-01-012023-03-310000776867wtm:BambooIde8InsuranceServicesLLCSegmentMemberus-gaap:OperatingSegmentsMember2024-01-012024-03-310000776867wtm:BambooIde8InsuranceServicesLLCSegmentMemberus-gaap:OperatingSegmentsMember2023-01-012023-03-310000776867us-gaap:CorporateNonSegmentMember2024-01-012024-03-310000776867us-gaap:CorporateNonSegmentMember2023-01-012023-03-310000776867wtm:InvestmentsExcludingMediaAlphaMemberus-gaap:CorporateNonSegmentMember2024-01-012024-03-310000776867wtm:InvestmentsExcludingMediaAlphaMemberus-gaap:CorporateNonSegmentMember2023-01-012023-03-310000776867wtm:MediaAlphaMemberus-gaap:CorporateNonSegmentMember2024-01-012024-03-310000776867wtm:MediaAlphaMemberus-gaap:CorporateNonSegmentMember2023-01-012023-03-3100007768672023-01-012023-03-310000776867us-gaap:CommonStockIncludingAdditionalPaidInCapitalMember2023-12-310000776867us-gaap:RetainedEarningsMember2023-12-310000776867us-gaap:AccumulatedOtherComprehensiveIncomeMember2023-12-310000776867us-gaap:ParentMember2023-12-310000776867us-gaap:NoncontrollingInterestMember2023-12-310000776867wtm:TotalEquityIncludingNoncontrollingInterestMember2023-12-310000776867us-gaap:RetainedEarningsMember2024-01-012024-03-310000776867us-gaap:ParentMember2024-01-012024-03-310000776867us-gaap:NoncontrollingInterestMember2024-01-012024-03-310000776867wtm:TotalEquityIncludingNoncontrollingInterestMember2024-01-012024-03-310000776867us-gaap:AccumulatedOtherComprehensiveIncomeMember2024-01-012024-03-310000776867us-gaap:CommonStockIncludingAdditionalPaidInCapitalMember2024-01-012024-03-310000776867us-gaap:CommonStockIncludingAdditionalPaidInCapitalMember2024-03-310000776867us-gaap:RetainedEarningsMember2024-03-310000776867us-gaap:AccumulatedOtherComprehensiveIncomeMember2024-03-310000776867us-gaap:ParentMember2024-03-310000776867us-gaap:NoncontrollingInterestMember2024-03-310000776867wtm:TotalEquityIncludingNoncontrollingInterestMember2024-03-310000776867us-gaap:CommonStockIncludingAdditionalPaidInCapitalMember2022-12-310000776867us-gaap:RetainedEarningsMember2022-12-310000776867us-gaap:AccumulatedOtherComprehensiveIncomeMember2022-12-310000776867us-gaap:ParentMember2022-12-310000776867us-gaap:NoncontrollingInterestMember2022-12-310000776867wtm:TotalEquityIncludingNoncontrollingInterestMember2022-12-310000776867us-gaap:RetainedEarningsMember2023-01-012023-03-310000776867us-gaap:ParentMember2023-01-012023-03-310000776867us-gaap:NoncontrollingInterestMember2023-01-012023-03-310000776867wtm:TotalEquityIncludingNoncontrollingInterestMember2023-01-012023-03-310000776867us-gaap:AccumulatedOtherComprehensiveIncomeMember2023-01-012023-03-310000776867us-gaap:CommonStockIncludingAdditionalPaidInCapitalMember2023-01-012023-03-310000776867us-gaap:CommonStockIncludingAdditionalPaidInCapitalMember2023-03-310000776867us-gaap:RetainedEarningsMember2023-03-310000776867us-gaap:AccumulatedOtherComprehensiveIncomeMember2023-03-310000776867us-gaap:ParentMember2023-03-310000776867us-gaap:NoncontrollingInterestMember2023-03-310000776867wtm:TotalEquityIncludingNoncontrollingInterestMember2023-03-310000776867wtm:InvestmentsExcludingMediaAlphaAndBambooMember2024-01-012024-03-310000776867wtm:InvestmentsExcludingMediaAlphaAndBambooMember2023-01-012023-03-310000776867wtm:MediaAlphaMember2024-01-012024-03-310000776867wtm:MediaAlphaMember2023-01-012023-03-3100007768672022-12-3100007768672023-03-310000776867wtm:SubsidiaryArkInsuranceHoldingsLimitedMember2024-03-310000776867wtm:SubsidiaryArkInsuranceHoldingsLimitedMember2023-12-310000776867us-gaap:PreferredStockMemberwtm:SubsidiaryWMOutriggerReMember2024-03-310000776867us-gaap:PreferredStockMemberwtm:SubsidiaryWMOutriggerReMember2023-12-310000776867srt:MaximumMemberwtm:SubsidiaryHGGlobalMember2024-03-310000776867wtm:SubsidiaryHGGlobalMember2024-01-012024-03-310000776867wtm:SubsidiaryHGGlobalMemberus-gaap:PreferredStockMember2024-03-310000776867wtm:SubsidiaryHGGlobalMemberus-gaap:PreferredStockMember2023-12-310000776867wtm:SubsidiaryHGGlobalMemberus-gaap:CommonStockMember2023-12-310000776867wtm:SubsidiaryKuduInvestmentManagementLLCMember2023-12-310000776867wtm:SubsidiaryKuduInvestmentManagementLLCMember2024-03-310000776867wtm:SubsidiaryBambooIde8InsuranceServicesLLCMember2023-12-310000776867wtm:SubsidiaryBambooIde8InsuranceServicesLLCMember2024-03-310000776867wtm:SubsidiaryWTMPartnersMember2023-10-250000776867wtm:BambooIde8InsuranceServicesLLCMember2024-01-022024-01-020000776867wtm:BambooIde8InsuranceServicesLLCMember2024-01-020000776867wtm:BambooIde8InsuranceServicesLLCMemberwtm:BambooManagementMember2024-01-020000776867wtm:BambooIde8InsuranceServicesLLCMember2024-01-020000776867wtm:BambooIde8InsuranceServicesLLCMember2024-03-310000776867wtm:OutriggerReMember2022-12-310000776867wtm:OutriggerReMember2022-10-012022-12-310000776867wtm:OutriggerReMember2023-10-012023-12-310000776867wtm:OutriggerReMember2024-03-310000776867wtm:OutriggerReMember2023-12-310000776867wtm:OutriggerReMember2024-01-012024-01-310000776867us-gaap:FixedMaturitiesMember2024-01-012024-03-310000776867us-gaap:FixedMaturitiesMember2023-01-012023-03-310000776867us-gaap:ShortTermInvestmentsMember2024-01-012024-03-310000776867us-gaap:ShortTermInvestmentsMember2023-01-012023-03-310000776867us-gaap:CommonStockMember2024-01-012024-03-310000776867us-gaap:CommonStockMember2023-01-012023-03-310000776867us-gaap:OtherLongTermInvestmentsMember2024-01-012024-03-310000776867us-gaap:OtherLongTermInvestmentsMember2023-01-012023-03-310000776867us-gaap:FixedMaturitiesMember2024-01-012024-03-310000776867us-gaap:FixedMaturitiesMember2023-01-012023-03-310000776867wtm:OtherShortTermInvestmentsMember2024-01-012024-03-310000776867wtm:OtherShortTermInvestmentsMember2023-01-012023-03-310000776867us-gaap:OtherLongTermInvestmentsMember2024-01-012024-03-310000776867us-gaap:OtherLongTermInvestmentsMember2023-01-012023-03-310000776867wtm:TotalInvestmentsBeforeTPCProvidersInvestmentsMember2024-01-012024-03-310000776867wtm:TotalInvestmentsBeforeTPCProvidersInvestmentsMember2023-01-012023-03-310000776867us-gaap:CommonStockMember2024-01-012024-03-310000776867us-gaap:CommonStockMember2023-01-012023-03-310000776867wtm:MediaAlphaMemberus-gaap:EquityMethodInvestmentsMember2024-01-012024-03-310000776867wtm:MediaAlphaMemberus-gaap:EquityMethodInvestmentsMember2023-01-012023-03-310000776867wtm:FixedMaturitiesAndOtherShortTermInvestmentsMember2024-01-012024-03-310000776867wtm:FixedMaturitiesAndOtherShortTermInvestmentsMember2023-01-012023-03-310000776867wtm:CommonStockAndEquityMethodInvestmentsMember2024-01-012024-03-310000776867wtm:CommonStockAndEquityMethodInvestmentsMember2023-01-012023-03-310000776867wtm:TotalInvestmentsAfterTPCProvidersInvestmentsMember2024-01-012024-03-310000776867wtm:TotalInvestmentsAfterTPCProvidersInvestmentsMember2023-01-012023-03-310000776867us-gaap:FairValueInputsLevel3Memberus-gaap:OtherLongTermInvestmentsMember2024-01-012024-03-310000776867us-gaap:FairValueInputsLevel3Memberus-gaap:OtherLongTermInvestmentsMember2023-01-012023-03-310000776867us-gaap:USTreasuryAndGovernmentMember2024-03-310000776867us-gaap:USTreasuryAndGovernmentMember2024-01-012024-03-310000776867us-gaap:CorporateDebtSecuritiesMember2024-03-310000776867us-gaap:CorporateDebtSecuritiesMember2024-01-012024-03-310000776867us-gaap:MunicipalBondsMember2024-03-310000776867us-gaap:MunicipalBondsMember2024-01-012024-03-310000776867us-gaap:AssetBackedSecuritiesMember2024-03-310000776867us-gaap:AssetBackedSecuritiesMember2024-01-012024-03-310000776867us-gaap:CollateralizedLoanObligationsMember2024-03-310000776867us-gaap:CollateralizedLoanObligationsMember2024-01-012024-03-310000776867us-gaap:FixedMaturitiesMember2024-03-310000776867us-gaap:USTreasuryAndGovernmentMember2023-12-310000776867us-gaap:USTreasuryAndGovernmentMember2023-01-012023-12-310000776867us-gaap:CorporateDebtSecuritiesMember2023-12-310000776867us-gaap:CorporateDebtSecuritiesMember2023-01-012023-12-310000776867us-gaap:MunicipalBondsMember2023-12-310000776867us-gaap:MunicipalBondsMember2023-01-012023-12-310000776867us-gaap:AssetBackedSecuritiesMember2023-12-310000776867us-gaap:AssetBackedSecuritiesMember2023-01-012023-12-310000776867us-gaap:CollateralizedLoanObligationsMember2023-12-310000776867us-gaap:CollateralizedLoanObligationsMember2023-01-012023-12-310000776867us-gaap:FixedMaturitiesMember2023-12-310000776867us-gaap:FixedMaturitiesMember2023-01-012023-12-310000776867wtm:FixedMaturitiesExcludingAssetBackedSecuritiesAndCollateralizedLoanObligationsMember2024-03-310000776867wtm:AssetBackedSecuritiesAndCollateralizedLoanObligationsMember2024-03-310000776867wtm:MediaAlphaMember2024-03-3100007768672023-01-012023-12-310000776867wtm:MediaAlphaMember2023-12-310000776867wtm:MediaAlphaMember2023-01-012023-12-310000776867us-gaap:USTreasuryAndGovernmentMemberus-gaap:FairValueMeasurementsRecurringMember2024-03-310000776867us-gaap:USTreasuryAndGovernmentMemberus-gaap:FairValueInputsLevel1Memberus-gaap:FairValueMeasurementsRecurringMember2024-03-310000776867us-gaap:USTreasuryAndGovernmentMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Member2024-03-310000776867us-gaap:USTreasuryAndGovernmentMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel3Member2024-03-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FinancialServicesSectorMemberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867us-gaap:FairValueInputsLevel1Memberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FinancialServicesSectorMemberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FinancialServicesSectorMemberus-gaap:FairValueInputsLevel2Memberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel3Memberus-gaap:FinancialServicesSectorMemberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:ConsumerSectorMemberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867us-gaap:FairValueInputsLevel1Memberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:ConsumerSectorMemberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Memberus-gaap:ConsumerSectorMemberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel3Memberus-gaap:ConsumerSectorMemberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867us-gaap:CommercialAndIndustrialSectorMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867us-gaap:CommercialAndIndustrialSectorMemberus-gaap:FairValueInputsLevel1Memberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867us-gaap:CommercialAndIndustrialSectorMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Memberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867us-gaap:CommercialAndIndustrialSectorMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel3Memberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:HealthcareSectorMemberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867us-gaap:FairValueInputsLevel1Memberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:HealthcareSectorMemberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Memberus-gaap:HealthcareSectorMemberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel3Memberus-gaap:HealthcareSectorMemberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:TechnologySectorMemberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867us-gaap:FairValueInputsLevel1Memberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:TechnologySectorMemberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Memberus-gaap:TechnologySectorMemberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel3Memberus-gaap:TechnologySectorMemberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867wtm:UtilitiesSectorMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867us-gaap:FairValueInputsLevel1Memberwtm:UtilitiesSectorMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867wtm:UtilitiesSectorMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Memberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867wtm:UtilitiesSectorMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel3Memberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867us-gaap:FairValueMeasurementsRecurringMemberwtm:CommunicationsSectorMemberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867us-gaap:FairValueInputsLevel1Memberus-gaap:FairValueMeasurementsRecurringMemberwtm:CommunicationsSectorMemberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Memberwtm:CommunicationsSectorMemberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel3Memberwtm:CommunicationsSectorMemberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:EnergySectorMemberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867us-gaap:FairValueInputsLevel1Memberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:EnergySectorMemberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Memberus-gaap:EnergySectorMemberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel3Memberus-gaap:EnergySectorMemberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867us-gaap:FairValueMeasurementsRecurringMemberwtm:MaterialsSectorMemberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867us-gaap:FairValueInputsLevel1Memberus-gaap:FairValueMeasurementsRecurringMemberwtm:MaterialsSectorMemberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Memberwtm:MaterialsSectorMemberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel3Memberwtm:MaterialsSectorMemberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867us-gaap:FairValueInputsLevel1Memberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Memberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel3Memberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867us-gaap:MunicipalBondsMemberus-gaap:FairValueMeasurementsRecurringMember2024-03-310000776867us-gaap:MunicipalBondsMemberus-gaap:FairValueInputsLevel1Memberus-gaap:FairValueMeasurementsRecurringMember2024-03-310000776867us-gaap:MunicipalBondsMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Member2024-03-310000776867us-gaap:MunicipalBondsMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel3Member2024-03-310000776867us-gaap:AssetBackedSecuritiesMemberus-gaap:FairValueMeasurementsRecurringMember2024-03-310000776867us-gaap:AssetBackedSecuritiesMemberus-gaap:FairValueInputsLevel1Memberus-gaap:FairValueMeasurementsRecurringMember2024-03-310000776867us-gaap:AssetBackedSecuritiesMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Member2024-03-310000776867us-gaap:AssetBackedSecuritiesMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel3Member2024-03-310000776867us-gaap:CollateralizedLoanObligationsMemberus-gaap:FairValueMeasurementsRecurringMember2024-03-310000776867us-gaap:CollateralizedLoanObligationsMemberus-gaap:FairValueInputsLevel1Memberus-gaap:FairValueMeasurementsRecurringMember2024-03-310000776867us-gaap:CollateralizedLoanObligationsMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Member2024-03-310000776867us-gaap:CollateralizedLoanObligationsMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel3Member2024-03-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FixedMaturitiesMember2024-03-310000776867us-gaap:FairValueInputsLevel1Memberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FixedMaturitiesMember2024-03-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Memberus-gaap:FixedMaturitiesMember2024-03-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel3Memberus-gaap:FixedMaturitiesMember2024-03-310000776867us-gaap:FairValueMeasurementsRecurringMemberwtm:OtherShortTermInvestmentsMember2024-03-310000776867us-gaap:FairValueInputsLevel1Memberus-gaap:FairValueMeasurementsRecurringMemberwtm:OtherShortTermInvestmentsMember2024-03-310000776867us-gaap:FairValueMeasurementsRecurringMemberwtm:OtherShortTermInvestmentsMemberus-gaap:FairValueInputsLevel2Member2024-03-310000776867us-gaap:FairValueMeasurementsRecurringMemberwtm:OtherShortTermInvestmentsMemberus-gaap:FairValueInputsLevel3Member2024-03-310000776867us-gaap:FairValueMeasurementsRecurringMemberwtm:CommonStockExchangeTradedFundsMember2024-03-310000776867us-gaap:FairValueInputsLevel1Memberus-gaap:FairValueMeasurementsRecurringMemberwtm:CommonStockExchangeTradedFundsMember2024-03-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Memberwtm:CommonStockExchangeTradedFundsMember2024-03-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel3Memberwtm:CommonStockExchangeTradedFundsMember2024-03-310000776867wtm:CommonStockOtherMemberus-gaap:FairValueMeasurementsRecurringMember2024-03-310000776867wtm:CommonStockOtherMemberus-gaap:FairValueInputsLevel1Memberus-gaap:FairValueMeasurementsRecurringMember2024-03-310000776867wtm:CommonStockOtherMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Member2024-03-310000776867wtm:CommonStockOtherMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel3Member2024-03-310000776867us-gaap:CommonStockMemberus-gaap:FairValueMeasurementsRecurringMember2024-03-310000776867us-gaap:CommonStockMemberus-gaap:FairValueInputsLevel1Memberus-gaap:FairValueMeasurementsRecurringMember2024-03-310000776867us-gaap:CommonStockMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Member2024-03-310000776867us-gaap:CommonStockMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel3Member2024-03-310000776867wtm:MediaAlphaMemberus-gaap:FairValueMeasurementsRecurringMember2024-03-310000776867wtm:MediaAlphaMemberus-gaap:FairValueInputsLevel1Memberus-gaap:FairValueMeasurementsRecurringMember2024-03-310000776867wtm:MediaAlphaMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Member2024-03-310000776867wtm:MediaAlphaMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel3Member2024-03-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel12And3Memberus-gaap:OtherLongTermInvestmentsMember2024-03-310000776867us-gaap:FairValueInputsLevel1Memberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:OtherLongTermInvestmentsMember2024-03-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Memberus-gaap:OtherLongTermInvestmentsMember2024-03-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel3Memberus-gaap:OtherLongTermInvestmentsMember2024-03-310000776867us-gaap:FairValueMeasuredAtNetAssetValuePerShareMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:OtherLongTermInvestmentsMember2024-03-310000776867wtm:TotalOtherLongTermInvestmentsMemberus-gaap:FairValueMeasurementsRecurringMember2024-03-310000776867wtm:TotalOtherLongTermInvestmentsMemberus-gaap:FairValueInputsLevel1Memberus-gaap:FairValueMeasurementsRecurringMember2024-03-310000776867wtm:TotalOtherLongTermInvestmentsMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Member2024-03-310000776867wtm:TotalOtherLongTermInvestmentsMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel3Member2024-03-310000776867us-gaap:FairValueMeasurementsRecurringMember2024-03-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel1Member2024-03-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Member2024-03-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel3Member2024-03-310000776867us-gaap:USTreasuryAndGovernmentMemberus-gaap:FairValueMeasurementsRecurringMember2023-12-310000776867us-gaap:USTreasuryAndGovernmentMemberus-gaap:FairValueInputsLevel1Memberus-gaap:FairValueMeasurementsRecurringMember2023-12-310000776867us-gaap:USTreasuryAndGovernmentMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Member2023-12-310000776867us-gaap:USTreasuryAndGovernmentMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel3Member2023-12-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FinancialServicesSectorMemberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867us-gaap:FairValueInputsLevel1Memberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FinancialServicesSectorMemberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FinancialServicesSectorMemberus-gaap:FairValueInputsLevel2Memberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel3Memberus-gaap:FinancialServicesSectorMemberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:ConsumerSectorMemberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867us-gaap:FairValueInputsLevel1Memberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:ConsumerSectorMemberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Memberus-gaap:ConsumerSectorMemberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel3Memberus-gaap:ConsumerSectorMemberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867us-gaap:CommercialAndIndustrialSectorMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867us-gaap:CommercialAndIndustrialSectorMemberus-gaap:FairValueInputsLevel1Memberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867us-gaap:CommercialAndIndustrialSectorMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Memberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867us-gaap:CommercialAndIndustrialSectorMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel3Memberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:HealthcareSectorMemberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867us-gaap:FairValueInputsLevel1Memberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:HealthcareSectorMemberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Memberus-gaap:HealthcareSectorMemberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel3Memberus-gaap:HealthcareSectorMemberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:TechnologySectorMemberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867us-gaap:FairValueInputsLevel1Memberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:TechnologySectorMemberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Memberus-gaap:TechnologySectorMemberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel3Memberus-gaap:TechnologySectorMemberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867wtm:UtilitiesSectorMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867us-gaap:FairValueInputsLevel1Memberwtm:UtilitiesSectorMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867wtm:UtilitiesSectorMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Memberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867wtm:UtilitiesSectorMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel3Memberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867us-gaap:FairValueMeasurementsRecurringMemberwtm:CommunicationsSectorMemberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867us-gaap:FairValueInputsLevel1Memberus-gaap:FairValueMeasurementsRecurringMemberwtm:CommunicationsSectorMemberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Memberwtm:CommunicationsSectorMemberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel3Memberwtm:CommunicationsSectorMemberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:EnergySectorMemberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867us-gaap:FairValueInputsLevel1Memberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:EnergySectorMemberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Memberus-gaap:EnergySectorMemberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel3Memberus-gaap:EnergySectorMemberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867us-gaap:FairValueMeasurementsRecurringMemberwtm:MaterialsSectorMemberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867us-gaap:FairValueInputsLevel1Memberus-gaap:FairValueMeasurementsRecurringMemberwtm:MaterialsSectorMemberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Memberwtm:MaterialsSectorMemberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel3Memberwtm:MaterialsSectorMemberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867us-gaap:FairValueInputsLevel1Memberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Memberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel3Memberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867us-gaap:MunicipalBondsMemberus-gaap:FairValueMeasurementsRecurringMember2023-12-310000776867us-gaap:MunicipalBondsMemberus-gaap:FairValueInputsLevel1Memberus-gaap:FairValueMeasurementsRecurringMember2023-12-310000776867us-gaap:MunicipalBondsMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Member2023-12-310000776867us-gaap:MunicipalBondsMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel3Member2023-12-310000776867us-gaap:AssetBackedSecuritiesMemberus-gaap:FairValueMeasurementsRecurringMember2023-12-310000776867us-gaap:AssetBackedSecuritiesMemberus-gaap:FairValueInputsLevel1Memberus-gaap:FairValueMeasurementsRecurringMember2023-12-310000776867us-gaap:AssetBackedSecuritiesMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Member2023-12-310000776867us-gaap:AssetBackedSecuritiesMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel3Member2023-12-310000776867us-gaap:CollateralizedLoanObligationsMemberus-gaap:FairValueMeasurementsRecurringMember2023-12-310000776867us-gaap:CollateralizedLoanObligationsMemberus-gaap:FairValueInputsLevel1Memberus-gaap:FairValueMeasurementsRecurringMember2023-12-310000776867us-gaap:CollateralizedLoanObligationsMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Member2023-12-310000776867us-gaap:CollateralizedLoanObligationsMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel3Member2023-12-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FixedMaturitiesMember2023-12-310000776867us-gaap:FairValueInputsLevel1Memberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FixedMaturitiesMember2023-12-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Memberus-gaap:FixedMaturitiesMember2023-12-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel3Memberus-gaap:FixedMaturitiesMember2023-12-310000776867us-gaap:FairValueMeasurementsRecurringMemberwtm:OtherShortTermInvestmentsMember2023-12-310000776867us-gaap:FairValueInputsLevel1Memberus-gaap:FairValueMeasurementsRecurringMemberwtm:OtherShortTermInvestmentsMember2023-12-310000776867us-gaap:FairValueMeasurementsRecurringMemberwtm:OtherShortTermInvestmentsMemberus-gaap:FairValueInputsLevel2Member2023-12-310000776867us-gaap:FairValueMeasurementsRecurringMemberwtm:OtherShortTermInvestmentsMemberus-gaap:FairValueInputsLevel3Member2023-12-310000776867us-gaap:FairValueMeasurementsRecurringMemberwtm:CommonStockExchangeTradedFundsMember2023-12-310000776867us-gaap:FairValueInputsLevel1Memberus-gaap:FairValueMeasurementsRecurringMemberwtm:CommonStockExchangeTradedFundsMember2023-12-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Memberwtm:CommonStockExchangeTradedFundsMember2023-12-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel3Memberwtm:CommonStockExchangeTradedFundsMember2023-12-310000776867wtm:CommonStockOtherMemberus-gaap:FairValueMeasurementsRecurringMember2023-12-310000776867wtm:CommonStockOtherMemberus-gaap:FairValueInputsLevel1Memberus-gaap:FairValueMeasurementsRecurringMember2023-12-310000776867wtm:CommonStockOtherMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Member2023-12-310000776867wtm:CommonStockOtherMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel3Member2023-12-310000776867us-gaap:CommonStockMemberus-gaap:FairValueMeasurementsRecurringMember2023-12-310000776867us-gaap:CommonStockMemberus-gaap:FairValueInputsLevel1Memberus-gaap:FairValueMeasurementsRecurringMember2023-12-310000776867us-gaap:CommonStockMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Member2023-12-310000776867us-gaap:CommonStockMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel3Member2023-12-310000776867wtm:MediaAlphaMemberus-gaap:FairValueMeasurementsRecurringMember2023-12-310000776867wtm:MediaAlphaMemberus-gaap:FairValueInputsLevel1Memberus-gaap:FairValueMeasurementsRecurringMember2023-12-310000776867wtm:MediaAlphaMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Member2023-12-310000776867wtm:MediaAlphaMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel3Member2023-12-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel12And3Memberus-gaap:OtherLongTermInvestmentsMember2023-12-310000776867us-gaap:FairValueInputsLevel1Memberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:OtherLongTermInvestmentsMember2023-12-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Memberus-gaap:OtherLongTermInvestmentsMember2023-12-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel3Memberus-gaap:OtherLongTermInvestmentsMember2023-12-310000776867us-gaap:FairValueMeasuredAtNetAssetValuePerShareMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:OtherLongTermInvestmentsMember2023-12-310000776867wtm:TotalOtherLongTermInvestmentsMemberus-gaap:FairValueMeasurementsRecurringMember2023-12-310000776867wtm:TotalOtherLongTermInvestmentsMemberus-gaap:FairValueInputsLevel1Memberus-gaap:FairValueMeasurementsRecurringMember2023-12-310000776867wtm:TotalOtherLongTermInvestmentsMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Member2023-12-310000776867wtm:TotalOtherLongTermInvestmentsMemberus-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel3Member2023-12-310000776867us-gaap:FairValueMeasurementsRecurringMember2023-12-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel1Member2023-12-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel2Member2023-12-310000776867us-gaap:FairValueMeasurementsRecurringMemberus-gaap:FairValueInputsLevel3Member2023-12-310000776867wtm:HGGlobalSeniorNotesMemberus-gaap:SeniorNotesMember2024-03-310000776867wtm:HGGlobalSeniorNotesMemberus-gaap:SeniorNotesMember2023-12-310000776867wtm:TrustDepositsMember2024-03-310000776867wtm:TrustDepositsMember2023-12-310000776867wtm:LloydsBankMember2024-03-310000776867wtm:LloydsBankMember2023-12-310000776867us-gaap:AssetPledgedAsCollateralMemberwtm:AdditionalInvestmentsInsuranceRegulatorsAndReinsuranceCounterpartiesMember2024-03-310000776867us-gaap:AssetPledgedAsCollateralMemberwtm:AdditionalInvestmentsInsuranceRegulatorsAndReinsuranceCounterpartiesMember2023-12-310000776867us-gaap:AssetPledgedAsCollateralMember2024-03-310000776867us-gaap:AssetPledgedAsCollateralMember2023-12-310000776867wtm:BambooCaptiveMember2024-03-310000776867us-gaap:SecuredDebtMemberwtm:KuduCreditFacilityMember2024-03-310000776867us-gaap:SecuredDebtMemberwtm:KuduCreditFacilityMember2023-12-310000776867srt:StandardPoorsAAARatingMemberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867srt:StandardPoorsAAARatingMemberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867srt:StandardPoorsAARatingMemberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867srt:StandardPoorsAARatingMemberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867srt:StandardPoorsARatingMemberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867srt:StandardPoorsARatingMemberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867srt:StandardPoorsBBBRatingMemberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867srt:StandardPoorsBBBRatingMemberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867srt:StandardPoorsBBRatingMemberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867srt:StandardPoorsBBRatingMemberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867wtm:StandardPoorsOtherMemberus-gaap:CorporateDebtSecuritiesMember2024-03-310000776867wtm:StandardPoorsOtherMemberus-gaap:CorporateDebtSecuritiesMember2023-12-310000776867us-gaap:MortgageBackedSecuritiesMemberus-gaap:FederalNationalMortgageAssociationCertificatesAndObligationsFNMAMember2024-03-310000776867us-gaap:MortgageBackedSecuritiesMemberus-gaap:FairValueInputsLevel2Memberus-gaap:FederalNationalMortgageAssociationCertificatesAndObligationsFNMAMember2024-03-310000776867us-gaap:MortgageBackedSecuritiesMemberus-gaap:FairValueInputsLevel3Memberus-gaap:FederalNationalMortgageAssociationCertificatesAndObligationsFNMAMember2024-03-310000776867us-gaap:MortgageBackedSecuritiesMemberus-gaap:FederalNationalMortgageAssociationCertificatesAndObligationsFNMAMember2023-12-310000776867us-gaap:MortgageBackedSecuritiesMemberus-gaap:FairValueInputsLevel2Memberus-gaap:FederalNationalMortgageAssociationCertificatesAndObligationsFNMAMember2023-12-310000776867us-gaap:MortgageBackedSecuritiesMemberus-gaap:FairValueInputsLevel3Memberus-gaap:FederalNationalMortgageAssociationCertificatesAndObligationsFNMAMember2023-12-310000776867us-gaap:MortgageBackedSecuritiesMemberus-gaap:FederalHomeLoanMortgageCorporationCertificatesAndObligationsFHLMCMember2024-03-310000776867us-gaap:MortgageBackedSecuritiesMemberus-gaap:FairValueInputsLevel2Memberus-gaap:FederalHomeLoanMortgageCorporationCertificatesAndObligationsFHLMCMember2024-03-310000776867us-gaap:MortgageBackedSecuritiesMemberus-gaap:FairValueInputsLevel3Memberus-gaap:FederalHomeLoanMortgageCorporationCertificatesAndObligationsFHLMCMember2024-03-310000776867us-gaap:MortgageBackedSecuritiesMemberus-gaap:FederalHomeLoanMortgageCorporationCertificatesAndObligationsFHLMCMember2023-12-310000776867us-gaap:MortgageBackedSecuritiesMemberus-gaap:FairValueInputsLevel2Memberus-gaap:FederalHomeLoanMortgageCorporationCertificatesAndObligationsFHLMCMember2023-12-310000776867us-gaap:MortgageBackedSecuritiesMemberus-gaap:FairValueInputsLevel3Memberus-gaap:FederalHomeLoanMortgageCorporationCertificatesAndObligationsFHLMCMember2023-12-310000776867us-gaap:MortgageBackedSecuritiesMemberus-gaap:GovernmentNationalMortgageAssociationCertificatesAndObligationsGNMAMember2024-03-310000776867us-gaap:MortgageBackedSecuritiesMemberus-gaap:FairValueInputsLevel2Memberus-gaap:GovernmentNationalMortgageAssociationCertificatesAndObligationsGNMAMember2024-03-310000776867us-gaap:MortgageBackedSecuritiesMemberus-gaap:FairValueInputsLevel3Memberus-gaap:GovernmentNationalMortgageAssociationCertificatesAndObligationsGNMAMember2024-03-310000776867us-gaap:MortgageBackedSecuritiesMemberus-gaap:GovernmentNationalMortgageAssociationCertificatesAndObligationsGNMAMember2023-12-310000776867us-gaap:MortgageBackedSecuritiesMemberus-gaap:FairValueInputsLevel2Memberus-gaap:GovernmentNationalMortgageAssociationCertificatesAndObligationsGNMAMember2023-12-310000776867us-gaap:MortgageBackedSecuritiesMemberus-gaap:FairValueInputsLevel3Memberus-gaap:GovernmentNationalMortgageAssociationCertificatesAndObligationsGNMAMember2023-12-310000776867us-gaap:MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMemberus-gaap:MortgageBackedSecuritiesMember2024-03-310000776867us-gaap:MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMemberus-gaap:MortgageBackedSecuritiesMemberus-gaap:FairValueInputsLevel2Member2024-03-310000776867us-gaap:MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMemberus-gaap:MortgageBackedSecuritiesMemberus-gaap:FairValueInputsLevel3Member2024-03-310000776867us-gaap:MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMemberus-gaap:MortgageBackedSecuritiesMember2023-12-310000776867us-gaap:MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMemberus-gaap:MortgageBackedSecuritiesMemberus-gaap:FairValueInputsLevel2Member2023-12-310000776867us-gaap:MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMemberus-gaap:MortgageBackedSecuritiesMemberus-gaap:FairValueInputsLevel3Member2023-12-310000776867us-gaap:MortgageBackedSecuritiesMemberus-gaap:ResidentialMortgageBackedSecuritiesMember2024-03-310000776867us-gaap:MortgageBackedSecuritiesMemberus-gaap:FairValueInputsLevel2Memberus-gaap:ResidentialMortgageBackedSecuritiesMember2024-03-310000776867us-gaap:MortgageBackedSecuritiesMemberus-gaap:FairValueInputsLevel3Memberus-gaap:ResidentialMortgageBackedSecuritiesMember2024-03-310000776867us-gaap:MortgageBackedSecuritiesMemberus-gaap:ResidentialMortgageBackedSecuritiesMember2023-12-310000776867us-gaap:MortgageBackedSecuritiesMemberus-gaap:FairValueInputsLevel2Memberus-gaap:ResidentialMortgageBackedSecuritiesMember2023-12-310000776867us-gaap:MortgageBackedSecuritiesMemberus-gaap:FairValueInputsLevel3Memberus-gaap:ResidentialMortgageBackedSecuritiesMember2023-12-310000776867us-gaap:MortgageBackedSecuritiesMemberus-gaap:MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember2024-03-310000776867us-gaap:MortgageBackedSecuritiesMemberus-gaap:MortgageBackedSecuritiesIssuedByPrivateEnterprisesMemberus-gaap:FairValueInputsLevel2Member2024-03-310000776867us-gaap:MortgageBackedSecuritiesMemberus-gaap:MortgageBackedSecuritiesIssuedByPrivateEnterprisesMemberus-gaap:FairValueInputsLevel3Member2024-03-310000776867us-gaap:MortgageBackedSecuritiesMemberus-gaap:MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember2023-12-310000776867us-gaap:MortgageBackedSecuritiesMemberus-gaap:MortgageBackedSecuritiesIssuedByPrivateEnterprisesMemberus-gaap:FairValueInputsLevel2Member2023-12-310000776867us-gaap:MortgageBackedSecuritiesMemberus-gaap:MortgageBackedSecuritiesIssuedByPrivateEnterprisesMemberus-gaap:FairValueInputsLevel3Member2023-12-310000776867us-gaap:MortgageBackedSecuritiesMember2024-03-310000776867us-gaap:MortgageBackedSecuritiesMemberus-gaap:FairValueInputsLevel2Member2024-03-310000776867us-gaap:MortgageBackedSecuritiesMemberus-gaap:FairValueInputsLevel3Member2024-03-310000776867us-gaap:MortgageBackedSecuritiesMember2023-12-310000776867us-gaap:MortgageBackedSecuritiesMemberus-gaap:FairValueInputsLevel2Member2023-12-310000776867us-gaap:MortgageBackedSecuritiesMemberus-gaap:FairValueInputsLevel3Member2023-12-310000776867us-gaap:AssetBackedSecuritiesSecuritizedLoansAndReceivablesMemberus-gaap:CollateralizedAutoLoansMember2024-03-310000776867us-gaap:AssetBackedSecuritiesSecuritizedLoansAndReceivablesMemberus-gaap:FairValueInputsLevel2Memberus-gaap:CollateralizedAutoLoansMember2024-03-310000776867us-gaap:FairValueInputsLevel3Memberus-gaap:AssetBackedSecuritiesSecuritizedLoansAndReceivablesMemberus-gaap:CollateralizedAutoLoansMember2024-03-310000776867us-gaap:AssetBackedSecuritiesSecuritizedLoansAndReceivablesMemberus-gaap:CollateralizedAutoLoansMember2023-12-310000776867us-gaap:AssetBackedSecuritiesSecuritizedLoansAndReceivablesMemberus-gaap:FairValueInputsLevel2Memberus-gaap:CollateralizedAutoLoansMember2023-12-310000776867us-gaap:FairValueInputsLevel3Memberus-gaap:AssetBackedSecuritiesSecuritizedLoansAndReceivablesMemberus-gaap:CollateralizedAutoLoansMember2023-12-310000776867us-gaap:CollateralizedCreditCardSecuritiesMemberus-gaap:AssetBackedSecuritiesSecuritizedLoansAndReceivablesMember2024-03-310000776867us-gaap:CollateralizedCreditCardSecuritiesMemberus-gaap:AssetBackedSecuritiesSecuritizedLoansAndReceivablesMemberus-gaap:FairValueInputsLevel2Member2024-03-310000776867us-gaap:CollateralizedCreditCardSecuritiesMemberus-gaap:FairValueInputsLevel3Memberus-gaap:AssetBackedSecuritiesSecuritizedLoansAndReceivablesMember2024-03-310000776867us-gaap:CollateralizedCreditCardSecuritiesMemberus-gaap:AssetBackedSecuritiesSecuritizedLoansAndReceivablesMember2023-12-310000776867us-gaap:CollateralizedCreditCardSecuritiesMemberus-gaap:AssetBackedSecuritiesSecuritizedLoansAndReceivablesMemberus-gaap:FairValueInputsLevel2Member2023-12-310000776867us-gaap:CollateralizedCreditCardSecuritiesMemberus-gaap:FairValueInputsLevel3Memberus-gaap:AssetBackedSecuritiesSecuritizedLoansAndReceivablesMember2023-12-310000776867us-gaap:AssetBackedSecuritiesSecuritizedLoansAndReceivablesMemberwtm:OtherAssetBackedSecuritiesMember2024-03-310000776867us-gaap:AssetBackedSecuritiesSecuritizedLoansAndReceivablesMemberus-gaap:FairValueInputsLevel2Memberwtm:OtherAssetBackedSecuritiesMember2024-03-310000776867us-gaap:FairValueInputsLevel3Memberus-gaap:AssetBackedSecuritiesSecuritizedLoansAndReceivablesMemberwtm:OtherAssetBackedSecuritiesMember2024-03-310000776867us-gaap:AssetBackedSecuritiesSecuritizedLoansAndReceivablesMemberwtm:OtherAssetBackedSecuritiesMember2023-12-310000776867us-gaap:AssetBackedSecuritiesSecuritizedLoansAndReceivablesMemberus-gaap:FairValueInputsLevel2Memberwtm:OtherAssetBackedSecuritiesMember2023-12-310000776867us-gaap:FairValueInputsLevel3Memberus-gaap:AssetBackedSecuritiesSecuritizedLoansAndReceivablesMemberwtm:OtherAssetBackedSecuritiesMember2023-12-310000776867us-gaap:AssetBackedSecuritiesSecuritizedLoansAndReceivablesMember2024-03-310000776867us-gaap:AssetBackedSecuritiesSecuritizedLoansAndReceivablesMemberus-gaap:FairValueInputsLevel2Member2024-03-310000776867us-gaap:FairValueInputsLevel3Memberus-gaap:AssetBackedSecuritiesSecuritizedLoansAndReceivablesMember2024-03-310000776867us-gaap:AssetBackedSecuritiesSecuritizedLoansAndReceivablesMember2023-12-310000776867us-gaap:AssetBackedSecuritiesSecuritizedLoansAndReceivablesMemberus-gaap:FairValueInputsLevel2Member2023-12-310000776867us-gaap:FairValueInputsLevel3Memberus-gaap:AssetBackedSecuritiesSecuritizedLoansAndReceivablesMember2023-12-310000776867us-gaap:AssetBackedSecuritiesMemberus-gaap:FairValueInputsLevel2Member2024-03-310000776867us-gaap:AssetBackedSecuritiesMemberus-gaap:FairValueInputsLevel3Member2024-03-310000776867us-gaap:AssetBackedSecuritiesMemberus-gaap:FairValueInputsLevel2Member2023-12-310000776867us-gaap:AssetBackedSecuritiesMemberus-gaap:FairValueInputsLevel3Member2023-12-310000776867us-gaap:CollateralizedLoanObligationsMemberus-gaap:FairValueInputsLevel2Member2024-03-310000776867us-gaap:CollateralizedLoanObligationsMemberus-gaap:FairValueInputsLevel3Member2024-03-310000776867us-gaap:CollateralizedLoanObligationsMemberus-gaap:FairValueInputsLevel2Member2023-12-310000776867us-gaap:CollateralizedLoanObligationsMemberus-gaap:FairValueInputsLevel3Member2023-12-310000776867wtm:MortgageAndAssetBackedSecuritiesAndCollateralizedLoanObligationsMember2024-03-310000776867wtm:MortgageAndAssetBackedSecuritiesAndCollateralizedLoanObligationsMemberus-gaap:FairValueInputsLevel2Member2024-03-310000776867wtm:MortgageAndAssetBackedSecuritiesAndCollateralizedLoanObligationsMemberus-gaap:FairValueInputsLevel3Member2024-03-310000776867wtm:MortgageAndAssetBackedSecuritiesAndCollateralizedLoanObligationsMember2023-12-310000776867wtm:MortgageAndAssetBackedSecuritiesAndCollateralizedLoanObligationsMemberus-gaap:FairValueInputsLevel2Member2023-12-310000776867wtm:MortgageAndAssetBackedSecuritiesAndCollateralizedLoanObligationsMemberus-gaap:FairValueInputsLevel3Member2023-12-310000776867wtm:MediaAlphaMember2023-04-012023-06-300000776867wtm:MediaAlphaMemberus-gaap:IPOMember2024-01-012024-03-310000776867wtm:MediaAlphaMember2024-03-282024-03-280000776867wtm:MediaAlphaMemberus-gaap:FairValueMeasurementsRecurringMember2024-03-280000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberwtm:KuduParticipationContractsMemberwtm:KuduInvestmentManagementLLCMemberus-gaap:OperatingSegmentsMember2024-03-310000776867wtm:KuduInvestmentManagementLLCSegmentMemberwtm:KuduParticipationContractsMemberwtm:KuduInvestmentManagementLLCMemberus-gaap:OperatingSegmentsMember2024-03-310000776867wtm:KuduParticipationContractsMemberwtm:KuduInvestmentManagementLLCMemberus-gaap:CorporateNonSegmentMember2024-03-310000776867wtm:KuduParticipationContractsMemberwtm:KuduInvestmentManagementLLCMember2024-03-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberwtm:DavidShieldPassportCardMemberus-gaap:OperatingSegmentsMember2024-03-310000776867wtm:DavidShieldPassportCardMemberwtm:KuduInvestmentManagementLLCSegmentMemberus-gaap:OperatingSegmentsMember2024-03-310000776867wtm:DavidShieldPassportCardMemberus-gaap:CorporateNonSegmentMember2024-03-310000776867wtm:DavidShieldPassportCardMember2024-03-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberwtm:ElementumHoldingsL.P.Memberus-gaap:OperatingSegmentsMember2024-03-310000776867wtm:KuduInvestmentManagementLLCSegmentMemberwtm:ElementumHoldingsL.P.Memberus-gaap:OperatingSegmentsMember2024-03-310000776867us-gaap:CorporateNonSegmentMemberwtm:ElementumHoldingsL.P.Member2024-03-310000776867wtm:ElementumHoldingsL.P.Member2024-03-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberwtm:OtherUnconsolidatedPrivateEquityInvestmentsMemberus-gaap:OperatingSegmentsMember2024-03-310000776867wtm:KuduInvestmentManagementLLCSegmentMemberwtm:OtherUnconsolidatedPrivateEquityInvestmentsMemberus-gaap:OperatingSegmentsMember2024-03-310000776867wtm:OtherUnconsolidatedPrivateEquityInvestmentsMemberus-gaap:CorporateNonSegmentMember2024-03-310000776867wtm:OtherUnconsolidatedPrivateEquityInvestmentsMember2024-03-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberwtm:TotalUnconsolidatedEntitiesMemberwtm:InvestmentsExcludingMediaAlphaMemberus-gaap:OperatingSegmentsMember2024-03-310000776867wtm:KuduInvestmentManagementLLCSegmentMemberwtm:TotalUnconsolidatedEntitiesMemberwtm:InvestmentsExcludingMediaAlphaMemberus-gaap:OperatingSegmentsMember2024-03-310000776867wtm:TotalUnconsolidatedEntitiesMemberwtm:InvestmentsExcludingMediaAlphaMemberus-gaap:CorporateNonSegmentMember2024-03-310000776867wtm:TotalUnconsolidatedEntitiesMemberwtm:InvestmentsExcludingMediaAlphaMember2024-03-310000776867wtm:PrivateEquityFundsAndHedgeFundsMemberwtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberus-gaap:OperatingSegmentsMember2024-03-310000776867wtm:PrivateEquityFundsAndHedgeFundsMemberwtm:KuduInvestmentManagementLLCSegmentMemberus-gaap:OperatingSegmentsMember2024-03-310000776867wtm:PrivateEquityFundsAndHedgeFundsMemberus-gaap:CorporateNonSegmentMember2024-03-310000776867wtm:PrivateEquityFundsAndHedgeFundsMember2024-03-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberwtm:BankLoanFundMemberus-gaap:OperatingSegmentsMember2024-03-310000776867wtm:BankLoanFundMemberwtm:KuduInvestmentManagementLLCSegmentMemberus-gaap:OperatingSegmentsMember2024-03-310000776867wtm:BankLoanFundMemberus-gaap:CorporateNonSegmentMember2024-03-310000776867wtm:BankLoanFundMember2024-03-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberwtm:TrustDepositsMemberus-gaap:OperatingSegmentsMember2024-03-310000776867wtm:KuduInvestmentManagementLLCSegmentMemberwtm:TrustDepositsMemberus-gaap:OperatingSegmentsMember2024-03-310000776867wtm:TrustDepositsMemberus-gaap:CorporateNonSegmentMember2024-03-310000776867wtm:TrustDepositsMember2024-03-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberwtm:InsuranceLinkedSecuritiesFundsMemberus-gaap:OperatingSegmentsMember2024-03-310000776867wtm:InsuranceLinkedSecuritiesFundsMemberwtm:KuduInvestmentManagementLLCSegmentMemberus-gaap:OperatingSegmentsMember2024-03-310000776867wtm:InsuranceLinkedSecuritiesFundsMemberus-gaap:CorporateNonSegmentMember2024-03-310000776867wtm:InsuranceLinkedSecuritiesFundsMember2024-03-310000776867wtm:PrivateDebtInstrumentMemberwtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberus-gaap:OperatingSegmentsMember2024-03-310000776867wtm:PrivateDebtInstrumentMemberwtm:KuduInvestmentManagementLLCSegmentMemberus-gaap:OperatingSegmentsMember2024-03-310000776867wtm:PrivateDebtInstrumentMemberus-gaap:CorporateNonSegmentMember2024-03-310000776867wtm:PrivateDebtInstrumentMember2024-03-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberwtm:OtherFundsMemberus-gaap:OperatingSegmentsMember2024-03-310000776867wtm:KuduInvestmentManagementLLCSegmentMemberwtm:OtherFundsMemberus-gaap:OperatingSegmentsMember2024-03-310000776867us-gaap:CorporateNonSegmentMemberwtm:OtherFundsMember2024-03-310000776867wtm:OtherFundsMember2024-03-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberwtm:KuduParticipationContractsMemberwtm:KuduInvestmentManagementLLCMemberus-gaap:OperatingSegmentsMember2023-12-310000776867wtm:KuduInvestmentManagementLLCSegmentMemberwtm:KuduParticipationContractsMemberwtm:KuduInvestmentManagementLLCMemberus-gaap:OperatingSegmentsMember2023-12-310000776867wtm:KuduParticipationContractsMemberwtm:KuduInvestmentManagementLLCMemberus-gaap:CorporateNonSegmentMember2023-12-310000776867wtm:KuduParticipationContractsMemberwtm:KuduInvestmentManagementLLCMember2023-12-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberwtm:DavidShieldPassportCardMemberus-gaap:OperatingSegmentsMember2023-12-310000776867wtm:DavidShieldPassportCardMemberwtm:KuduInvestmentManagementLLCSegmentMemberus-gaap:OperatingSegmentsMember2023-12-310000776867wtm:DavidShieldPassportCardMemberus-gaap:CorporateNonSegmentMember2023-12-310000776867wtm:DavidShieldPassportCardMember2023-12-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberwtm:ElementumHoldingsL.P.Memberus-gaap:OperatingSegmentsMember2023-12-310000776867wtm:KuduInvestmentManagementLLCSegmentMemberwtm:ElementumHoldingsL.P.Memberus-gaap:OperatingSegmentsMember2023-12-310000776867us-gaap:CorporateNonSegmentMemberwtm:ElementumHoldingsL.P.Member2023-12-310000776867wtm:ElementumHoldingsL.P.Member2023-12-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberwtm:OtherUnconsolidatedPrivateEquityInvestmentsMemberus-gaap:OperatingSegmentsMember2023-12-310000776867wtm:KuduInvestmentManagementLLCSegmentMemberwtm:OtherUnconsolidatedPrivateEquityInvestmentsMemberus-gaap:OperatingSegmentsMember2023-12-310000776867wtm:OtherUnconsolidatedPrivateEquityInvestmentsMemberus-gaap:CorporateNonSegmentMember2023-12-310000776867wtm:OtherUnconsolidatedPrivateEquityInvestmentsMember2023-12-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberwtm:TotalUnconsolidatedEntitiesMemberwtm:InvestmentsExcludingMediaAlphaMemberus-gaap:OperatingSegmentsMember2023-12-310000776867wtm:KuduInvestmentManagementLLCSegmentMemberwtm:TotalUnconsolidatedEntitiesMemberwtm:InvestmentsExcludingMediaAlphaMemberus-gaap:OperatingSegmentsMember2023-12-310000776867wtm:TotalUnconsolidatedEntitiesMemberwtm:InvestmentsExcludingMediaAlphaMemberus-gaap:CorporateNonSegmentMember2023-12-310000776867wtm:TotalUnconsolidatedEntitiesMemberwtm:InvestmentsExcludingMediaAlphaMember2023-12-310000776867wtm:PrivateEquityFundsAndHedgeFundsMemberwtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberus-gaap:OperatingSegmentsMember2023-12-310000776867wtm:PrivateEquityFundsAndHedgeFundsMemberwtm:KuduInvestmentManagementLLCSegmentMemberus-gaap:OperatingSegmentsMember2023-12-310000776867wtm:PrivateEquityFundsAndHedgeFundsMemberus-gaap:CorporateNonSegmentMember2023-12-310000776867wtm:PrivateEquityFundsAndHedgeFundsMember2023-12-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberwtm:BankLoanFundMemberus-gaap:OperatingSegmentsMember2023-12-310000776867wtm:BankLoanFundMemberwtm:KuduInvestmentManagementLLCSegmentMemberus-gaap:OperatingSegmentsMember2023-12-310000776867wtm:BankLoanFundMemberus-gaap:CorporateNonSegmentMember2023-12-310000776867wtm:BankLoanFundMember2023-12-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberwtm:TrustDepositsMemberus-gaap:OperatingSegmentsMember2023-12-310000776867wtm:KuduInvestmentManagementLLCSegmentMemberwtm:TrustDepositsMemberus-gaap:OperatingSegmentsMember2023-12-310000776867wtm:TrustDepositsMemberus-gaap:CorporateNonSegmentMember2023-12-310000776867wtm:TrustDepositsMember2023-12-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberwtm:InsuranceLinkedSecuritiesFundsMemberus-gaap:OperatingSegmentsMember2023-12-310000776867wtm:InsuranceLinkedSecuritiesFundsMemberwtm:KuduInvestmentManagementLLCSegmentMemberus-gaap:OperatingSegmentsMember2023-12-310000776867wtm:InsuranceLinkedSecuritiesFundsMemberus-gaap:CorporateNonSegmentMember2023-12-310000776867wtm:InsuranceLinkedSecuritiesFundsMember2023-12-310000776867wtm:PrivateDebtInstrumentMemberwtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberus-gaap:OperatingSegmentsMember2023-12-310000776867wtm:PrivateDebtInstrumentMemberwtm:KuduInvestmentManagementLLCSegmentMemberus-gaap:OperatingSegmentsMember2023-12-310000776867wtm:PrivateDebtInstrumentMemberus-gaap:CorporateNonSegmentMember2023-12-310000776867wtm:PrivateDebtInstrumentMember2023-12-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberwtm:OtherFundsMemberus-gaap:OperatingSegmentsMember2023-12-310000776867wtm:KuduInvestmentManagementLLCSegmentMemberwtm:OtherFundsMemberus-gaap:OperatingSegmentsMember2023-12-310000776867us-gaap:CorporateNonSegmentMemberwtm:OtherFundsMember2023-12-310000776867wtm:OtherFundsMember2023-12-310000776867us-gaap:PrivateEquityFundsMember2024-03-310000776867us-gaap:HedgeFundsMember2024-03-310000776867wtm:PrivateEquityAndHedgeFundConcentrationRiskMemberus-gaap:InvestmentsMemberwtm:LargestInvestmentMember2024-03-310000776867wtm:PrivateEquityAndHedgeFundConcentrationRiskMemberus-gaap:InvestmentsMemberwtm:LargestInvestmentMember2023-12-310000776867wtm:AerospaceDefenseGovernmentSectorMemberus-gaap:PrivateEquityFundsMember2024-03-310000776867wtm:AerospaceDefenseGovernmentSectorMemberus-gaap:PrivateEquityFundsMember2023-12-310000776867us-gaap:FinancialServicesSectorMemberus-gaap:PrivateEquityFundsMember2024-03-310000776867us-gaap:FinancialServicesSectorMemberus-gaap:PrivateEquityFundsMember2023-12-310000776867us-gaap:RealEstateSectorMemberus-gaap:PrivateEquityFundsMember2024-03-310000776867us-gaap:RealEstateSectorMemberus-gaap:PrivateEquityFundsMember2023-12-310000776867us-gaap:PrivateEquityFundsMember2023-12-310000776867us-gaap:HedgeFundsMemberwtm:HedgeFundLongShortEquityBanksAndFinancialMember2024-03-310000776867us-gaap:HedgeFundsMemberwtm:HedgeFundLongShortEquityBanksAndFinancialMember2023-12-310000776867us-gaap:HedgeFundsMemberwtm:HedgeFundEuropeanSmallMidCapMember2024-03-310000776867us-gaap:HedgeFundsMemberwtm:HedgeFundEuropeanSmallMidCapMember2023-12-310000776867us-gaap:HedgeFundsMember2023-12-310000776867wtm:PrivateEquityFundsAndHedgeFundsMember2024-03-310000776867wtm:PrivateEquityFundsAndHedgeFundsMember2023-12-310000776867us-gaap:HedgeFundsMembersrt:MinimumMember2024-01-012024-03-310000776867us-gaap:HedgeFundsMembersrt:MaximumMember2024-01-012024-03-310000776867wtm:ForeignRegulatoryDepositsMember2024-03-310000776867wtm:ForeignRegulatoryDepositsMember2023-12-310000776867wtm:InsuranceLinkedSecuritiesFundsMembersrt:MinimumMember2024-01-012024-03-310000776867wtm:InsuranceLinkedSecuritiesFundsMembersrt:MaximumMember2024-01-012024-03-310000776867us-gaap:OtherLongTermInvestmentsMember2023-12-310000776867us-gaap:OtherLongTermInvestmentsMember2022-12-310000776867us-gaap:OtherLongTermInvestmentsMember2024-03-310000776867us-gaap:OtherLongTermInvestmentsMember2023-03-310000776867wtm:ValuationTechniqueRecentOrExpectedTransactionPricesMemberus-gaap:FairValueInputsLevel3Member2024-03-310000776867wtm:ValuationTechniqueRecentOrExpectedTransactionPricesMemberus-gaap:FairValueInputsLevel3Member2023-12-310000776867wtm:KuduParticipationContractsMemberus-gaap:FairValueInputsLevel3Memberus-gaap:ValuationTechniqueDiscountedCashFlowMember2024-03-310000776867us-gaap:MeasurementInputDiscountRateMemberwtm:KuduParticipationContractsMemberus-gaap:FairValueInputsLevel3Memberus-gaap:ValuationTechniqueDiscountedCashFlowMembersrt:MinimumMember2024-01-012024-03-310000776867us-gaap:MeasurementInputDiscountRateMemberwtm:KuduParticipationContractsMembersrt:MaximumMemberus-gaap:FairValueInputsLevel3Memberus-gaap:ValuationTechniqueDiscountedCashFlowMember2024-01-012024-03-310000776867wtm:KuduParticipationContractsMemberus-gaap:FairValueInputsLevel3Memberus-gaap:ValuationTechniqueDiscountedCashFlowMembersrt:MinimumMemberwtm:MeasurementInputTerminalCashFlowExitMultipleMember2024-01-012024-03-310000776867wtm:KuduParticipationContractsMembersrt:MaximumMemberus-gaap:FairValueInputsLevel3Memberus-gaap:ValuationTechniqueDiscountedCashFlowMemberwtm:MeasurementInputTerminalCashFlowExitMultipleMember2024-01-012024-03-310000776867wtm:DavidShieldPassportCardMemberus-gaap:FairValueInputsLevel3Memberus-gaap:ValuationTechniqueDiscountedCashFlowMember2024-03-310000776867us-gaap:MeasurementInputDiscountRateMemberwtm:DavidShieldPassportCardMemberus-gaap:FairValueInputsLevel3Memberus-gaap:ValuationTechniqueDiscountedCashFlowMember2024-01-012024-03-310000776867us-gaap:MeasurementInputLongTermRevenueGrowthRateMemberwtm:DavidShieldPassportCardMemberus-gaap:FairValueInputsLevel3Memberus-gaap:ValuationTechniqueDiscountedCashFlowMember2024-01-012024-03-310000776867us-gaap:FairValueInputsLevel3Memberwtm:ElementumHoldingsL.P.Memberus-gaap:ValuationTechniqueDiscountedCashFlowMember2024-03-310000776867us-gaap:MeasurementInputDiscountRateMemberus-gaap:FairValueInputsLevel3Memberwtm:ElementumHoldingsL.P.Memberus-gaap:ValuationTechniqueDiscountedCashFlowMember2024-01-012024-03-310000776867us-gaap:MeasurementInputLongTermRevenueGrowthRateMemberus-gaap:FairValueInputsLevel3Memberwtm:ElementumHoldingsL.P.Memberus-gaap:ValuationTechniqueDiscountedCashFlowMember2024-01-012024-03-310000776867us-gaap:FairValueInputsLevel3Memberwtm:MandatorilyRedeemablePreferredSecuritiesMemberus-gaap:ValuationTechniqueDiscountedCashFlowMember2024-03-310000776867us-gaap:MeasurementInputDiscountRateMemberus-gaap:FairValueInputsLevel3Memberwtm:MandatorilyRedeemablePreferredSecuritiesMemberus-gaap:ValuationTechniqueDiscountedCashFlowMember2024-01-012024-03-310000776867us-gaap:FairValueInputsLevel3Memberus-gaap:ValuationTechniqueDiscountedCashFlowMember2024-03-310000776867us-gaap:MeasurementInputDiscountRateMemberus-gaap:FairValueInputsLevel3Memberus-gaap:ValuationTechniqueDiscountedCashFlowMembersrt:MinimumMember2024-01-012024-03-310000776867us-gaap:MeasurementInputDiscountRateMemberus-gaap:FairValueInputsLevel3Membersrt:MaximumMemberus-gaap:ValuationTechniqueDiscountedCashFlowMember2024-01-012024-03-310000776867wtm:KuduParticipationContractsMemberus-gaap:FairValueInputsLevel3Memberus-gaap:ValuationTechniqueDiscountedCashFlowMemberwtm:MeasurementInputPreTaxDiscountRateMember2024-01-012024-03-310000776867wtm:KuduParticipationContractsMemberus-gaap:FairValueInputsLevel3Memberwtm:MeasurementInputPreTaxTerminalCashFlowExitMultipleMemberus-gaap:ValuationTechniqueDiscountedCashFlowMember2024-01-012024-03-310000776867wtm:ValuationTechniqueProbabilityWeightedExpectedReturnMemberwtm:KuduParticipationContractsMemberus-gaap:FairValueInputsLevel3Member2024-03-310000776867wtm:KuduParticipationContractsMemberus-gaap:FairValueInputsLevel3Memberus-gaap:ValuationTechniqueDiscountedCashFlowMember2023-12-310000776867us-gaap:MeasurementInputDiscountRateMemberwtm:KuduParticipationContractsMemberus-gaap:FairValueInputsLevel3Memberus-gaap:ValuationTechniqueDiscountedCashFlowMembersrt:MinimumMember2023-01-012023-12-310000776867us-gaap:MeasurementInputDiscountRateMemberwtm:KuduParticipationContractsMembersrt:MaximumMemberus-gaap:FairValueInputsLevel3Memberus-gaap:ValuationTechniqueDiscountedCashFlowMember2023-01-012023-12-310000776867wtm:KuduParticipationContractsMemberus-gaap:FairValueInputsLevel3Memberus-gaap:ValuationTechniqueDiscountedCashFlowMembersrt:MinimumMemberwtm:MeasurementInputTerminalCashFlowExitMultipleMember2023-01-012023-12-310000776867wtm:KuduParticipationContractsMembersrt:MaximumMemberus-gaap:FairValueInputsLevel3Memberus-gaap:ValuationTechniqueDiscountedCashFlowMemberwtm:MeasurementInputTerminalCashFlowExitMultipleMember2023-01-012023-12-310000776867wtm:DavidShieldPassportCardMemberus-gaap:FairValueInputsLevel3Memberus-gaap:ValuationTechniqueDiscountedCashFlowMember2023-12-310000776867us-gaap:MeasurementInputDiscountRateMemberwtm:DavidShieldPassportCardMemberus-gaap:FairValueInputsLevel3Memberus-gaap:ValuationTechniqueDiscountedCashFlowMember2023-01-012023-12-310000776867us-gaap:MeasurementInputLongTermRevenueGrowthRateMemberwtm:DavidShieldPassportCardMemberus-gaap:FairValueInputsLevel3Memberus-gaap:ValuationTechniqueDiscountedCashFlowMember2023-01-012023-12-310000776867us-gaap:FairValueInputsLevel3Memberwtm:ElementumHoldingsL.P.Memberus-gaap:ValuationTechniqueDiscountedCashFlowMember2023-12-310000776867us-gaap:MeasurementInputDiscountRateMemberus-gaap:FairValueInputsLevel3Memberwtm:ElementumHoldingsL.P.Memberus-gaap:ValuationTechniqueDiscountedCashFlowMember2023-01-012023-12-310000776867us-gaap:MeasurementInputLongTermRevenueGrowthRateMemberus-gaap:FairValueInputsLevel3Memberwtm:ElementumHoldingsL.P.Memberus-gaap:ValuationTechniqueDiscountedCashFlowMember2023-01-012023-12-310000776867us-gaap:FairValueInputsLevel3Memberwtm:MandatorilyRedeemablePreferredSecuritiesMemberus-gaap:ValuationTechniqueDiscountedCashFlowMember2023-12-310000776867us-gaap:MeasurementInputDiscountRateMemberus-gaap:FairValueInputsLevel3Memberwtm:MandatorilyRedeemablePreferredSecuritiesMemberus-gaap:ValuationTechniqueDiscountedCashFlowMember2023-01-012023-12-310000776867us-gaap:FairValueInputsLevel3Memberus-gaap:ValuationTechniqueDiscountedCashFlowMember2023-12-310000776867us-gaap:MeasurementInputDiscountRateMemberus-gaap:FairValueInputsLevel3Memberus-gaap:ValuationTechniqueDiscountedCashFlowMembersrt:MinimumMember2023-01-012023-12-310000776867us-gaap:MeasurementInputDiscountRateMemberus-gaap:FairValueInputsLevel3Membersrt:MaximumMemberus-gaap:ValuationTechniqueDiscountedCashFlowMember2023-01-012023-12-310000776867wtm:KuduParticipationContractsMemberus-gaap:FairValueInputsLevel3Memberus-gaap:ValuationTechniqueDiscountedCashFlowMemberwtm:MeasurementInputPreTaxDiscountRateMember2023-01-012023-06-300000776867wtm:KuduParticipationContractsMemberus-gaap:FairValueInputsLevel3Memberwtm:MeasurementInputPreTaxTerminalCashFlowExitMultipleMemberus-gaap:ValuationTechniqueDiscountedCashFlowMember2023-01-012023-06-300000776867wtm:KuduParticipationContractsMember2023-01-012023-12-310000776867wtm:ValuationTechniqueProbabilityWeightedExpectedReturnMemberwtm:KuduParticipationContractsMemberus-gaap:FairValueInputsLevel3Member2023-12-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberwtm:ArkInsuranceHoldingsLimitedSegmentMemberus-gaap:OperatingSegmentsMember2024-03-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberwtm:ArkInsuranceHoldingsLimitedSegmentMemberus-gaap:OperatingSegmentsMember2023-12-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberwtm:ArkInsuranceHoldingsLimitedSegmentMemberwtm:UnderwritingCapacityMemberus-gaap:OperatingSegmentsMember2024-03-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberwtm:ArkInsuranceHoldingsLimitedSegmentMemberwtm:UnderwritingCapacityMemberus-gaap:OperatingSegmentsMember2023-12-310000776867wtm:KuduInvestmentManagementLLCSegmentMemberus-gaap:TradeNamesMemberus-gaap:OperatingSegmentsMember2024-01-012024-03-310000776867wtm:KuduInvestmentManagementLLCSegmentMemberus-gaap:TradeNamesMemberus-gaap:OperatingSegmentsMember2024-03-310000776867wtm:KuduInvestmentManagementLLCSegmentMemberus-gaap:TradeNamesMemberus-gaap:OperatingSegmentsMember2023-12-310000776867wtm:BambooIde8InsuranceServicesLLCSegmentMemberus-gaap:TradeNamesMemberus-gaap:OperatingSegmentsMember2024-01-012024-03-310000776867wtm:BambooIde8InsuranceServicesLLCSegmentMemberus-gaap:TradeNamesMemberus-gaap:OperatingSegmentsMember2024-03-310000776867wtm:BambooIde8InsuranceServicesLLCSegmentMemberus-gaap:TradeNamesMemberus-gaap:OperatingSegmentsMember2023-12-310000776867wtm:BambooIde8InsuranceServicesLLCSegmentMemberwtm:AgencyRelationshipsMemberus-gaap:OperatingSegmentsMember2024-01-012024-03-310000776867wtm:BambooIde8InsuranceServicesLLCSegmentMemberwtm:AgencyRelationshipsMemberus-gaap:OperatingSegmentsMember2024-03-310000776867wtm:BambooIde8InsuranceServicesLLCSegmentMemberwtm:AgencyRelationshipsMemberus-gaap:OperatingSegmentsMember2023-12-310000776867wtm:BambooIde8InsuranceServicesLLCSegmentMemberus-gaap:DevelopedTechnologyRightsMemberus-gaap:OperatingSegmentsMember2024-01-012024-03-310000776867wtm:BambooIde8InsuranceServicesLLCSegmentMemberus-gaap:DevelopedTechnologyRightsMemberus-gaap:OperatingSegmentsMember2024-03-310000776867wtm:BambooIde8InsuranceServicesLLCSegmentMemberus-gaap:DevelopedTechnologyRightsMemberus-gaap:OperatingSegmentsMember2023-12-310000776867wtm:BambooIde8InsuranceServicesLLCSegmentMemberus-gaap:OtherIntangibleAssetsMemberus-gaap:OperatingSegmentsMember2024-01-012024-03-310000776867wtm:BambooIde8InsuranceServicesLLCSegmentMemberus-gaap:OtherIntangibleAssetsMemberus-gaap:OperatingSegmentsMember2024-03-310000776867wtm:BambooIde8InsuranceServicesLLCSegmentMemberus-gaap:OtherIntangibleAssetsMemberus-gaap:OperatingSegmentsMember2023-12-310000776867us-gaap:CorporateNonSegmentMemberus-gaap:TradeNamesMember2024-01-012024-03-310000776867us-gaap:CorporateNonSegmentMemberus-gaap:TradeNamesMember2024-03-310000776867us-gaap:CorporateNonSegmentMemberus-gaap:TradeNamesMember2023-12-310000776867us-gaap:CustomerRelationshipsMemberus-gaap:CorporateNonSegmentMember2024-01-012024-03-310000776867us-gaap:CustomerRelationshipsMemberus-gaap:CorporateNonSegmentMember2024-03-310000776867us-gaap:CustomerRelationshipsMemberus-gaap:CorporateNonSegmentMember2023-12-310000776867us-gaap:OtherIntangibleAssetsMemberus-gaap:CorporateNonSegmentMember2024-01-012024-03-310000776867us-gaap:OtherIntangibleAssetsMemberus-gaap:CorporateNonSegmentMember2024-03-310000776867us-gaap:OtherIntangibleAssetsMemberus-gaap:CorporateNonSegmentMember2023-12-310000776867us-gaap:OtherIntangibleAssetsMember2024-03-310000776867us-gaap:OtherIntangibleAssetsMember2023-12-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMember2023-12-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMember2022-12-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMember2024-01-012024-03-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMember2023-01-012023-03-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMember2024-03-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMember2023-03-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberwtm:TPCProvidersMember2022-12-310000776867wtm:SyndicateArkInsuranceHoldingsLimitedMember2020-12-310000776867wtm:SyndicateArkInsuranceHoldingsLimitedMember2021-12-310000776867wtm:ArkInsuranceHoldingsLimitedOutriggerMember2024-01-012024-03-310000776867wtm:ArkInsuranceHoldingsLimitedOutriggerMember2023-01-012023-03-310000776867wtm:ArkInsuranceHoldingsLimitedSegmentMemberwtm:ArkInsuranceHoldingsLimitedOutriggerMember2024-01-012024-03-310000776867wtm:ArkInsuranceHoldingsLimitedSegmentMemberwtm:ArkInsuranceHoldingsLimitedOutriggerMember2023-01-012023-03-310000776867wtm:ArkInsuranceHoldingsLimitedOutriggerMember2024-03-310000776867wtm:ArkInsuranceHoldingsLimitedOutriggerMember2023-12-310000776867wtm:ArkInsuranceHoldingsLimitedSegmentMemberwtm:ArkInsuranceHoldingsLimitedOutriggerMember2024-03-310000776867wtm:ArkInsuranceHoldingsLimitedSegmentMemberwtm:ArkInsuranceHoldingsLimitedOutriggerMember2023-12-310000776867srt:AMBestAPlusRatingMemberwtm:ArkInsuranceHoldingsLimitedOutriggerMember2024-03-310000776867us-gaap:CededCreditRiskSecuredMembersrt:AMBestAPlusRatingMemberwtm:ArkInsuranceHoldingsLimitedOutriggerMember2024-03-310000776867srt:AMBestAPlusRatingMemberus-gaap:ReinsuranceRecoverableMemberus-gaap:ReinsurerConcentrationRiskMemberwtm:ArkInsuranceHoldingsLimitedOutriggerMember2024-01-012024-03-310000776867srt:AMBestAMinusRatingMemberwtm:ArkInsuranceHoldingsLimitedOutriggerMember2024-03-310000776867us-gaap:CededCreditRiskSecuredMembersrt:AMBestAMinusRatingMemberwtm:ArkInsuranceHoldingsLimitedOutriggerMember2024-03-310000776867us-gaap:ReinsuranceRecoverableMembersrt:AMBestAMinusRatingMemberus-gaap:ReinsurerConcentrationRiskMemberwtm:ArkInsuranceHoldingsLimitedOutriggerMember2024-01-012024-03-310000776867wtm:ArkInsuranceHoldingsLimitedOutriggerMembersrt:AMBestBPlusPlusRatingMember2024-03-310000776867us-gaap:CededCreditRiskSecuredMembersrt:AMBestBPlusPlusRatingMemberwtm:ArkInsuranceHoldingsLimitedOutriggerMember2024-03-310000776867us-gaap:ReinsuranceRecoverableMemberus-gaap:ReinsurerConcentrationRiskMembersrt:AMBestBPlusPlusRatingMemberwtm:ArkInsuranceHoldingsLimitedOutriggerMember2024-01-012024-03-310000776867us-gaap:CededCreditRiskSecuredMemberwtm:ArkInsuranceHoldingsLimitedOutriggerMember2024-03-310000776867us-gaap:ReinsuranceRecoverableMemberus-gaap:ReinsurerConcentrationRiskMemberwtm:ArkInsuranceHoldingsLimitedOutriggerMember2024-01-012024-03-310000776867wtm:ThirdPointReMemberwtm:ArkInsuranceHoldingsLimitedOutriggerMember2024-03-310000776867wtm:ThirdPointReMemberwtm:ArkInsuranceHoldingsLimitedOutriggerMember2023-12-310000776867wtm:Ark2007NotesMemberwtm:ArkSubordinatedNotesMemberus-gaap:SubordinatedDebtMember2024-03-310000776867wtm:Ark2007NotesMemberwtm:ArkSubordinatedNotesMemberus-gaap:SubordinatedDebtMember2023-12-310000776867us-gaap:SubordinatedDebtMemberwtm:Ark2021SubordinatedNotesTranche1Member2024-03-310000776867us-gaap:SubordinatedDebtMemberwtm:Ark2021SubordinatedNotesTranche1Member2023-12-310000776867us-gaap:SubordinatedDebtMemberwtm:Ark2021SubordinatedNotesTranche2Member2024-03-310000776867us-gaap:SubordinatedDebtMemberwtm:Ark2021SubordinatedNotesTranche2Member2023-12-310000776867wtm:Ark2021SubordinatedNotesTranche3Memberus-gaap:SubordinatedDebtMember2024-03-310000776867wtm:Ark2021SubordinatedNotesTranche3Memberus-gaap:SubordinatedDebtMember2023-12-310000776867us-gaap:SubordinatedDebtMemberwtm:Ark2021SubordinatedNotesMember2024-03-310000776867us-gaap:SubordinatedDebtMemberwtm:Ark2021SubordinatedNotesMember2023-12-310000776867wtm:ArkInsuranceHoldingsLimitedMemberus-gaap:SubordinatedDebtMember2024-03-310000776867wtm:ArkInsuranceHoldingsLimitedMemberus-gaap:SubordinatedDebtMember2023-12-310000776867wtm:KuduCreditFacilityMember2024-03-310000776867wtm:KuduCreditFacilityMember2023-12-310000776867wtm:OtherOperationsDebtMemberus-gaap:SecuredDebtMember2024-03-310000776867wtm:OtherOperationsDebtMemberus-gaap:SecuredDebtMember2023-12-310000776867wtm:OtherOperationsDebtMember2024-03-310000776867wtm:OtherOperationsDebtMember2023-12-310000776867us-gaap:JuniorSubordinatedDebtMemberwtm:Ark2007SubordinatedNotesMember2007-03-310000776867wtm:LondonInterbankOfferedRateLIBOR1Memberus-gaap:JuniorSubordinatedDebtMemberwtm:Ark2007SubordinatedNotesMember2007-03-012007-03-310000776867us-gaap:JuniorSubordinatedDebtMemberwtm:Ark2007SubordinatedNotesMember2024-01-012024-03-310000776867us-gaap:SubordinatedDebtMemberwtm:Ark2021SubordinatedNotesMember2021-09-300000776867us-gaap:SubordinatedDebtMemberwtm:Ark2021SubordinatedNotesMember2021-07-012021-09-300000776867us-gaap:SubordinatedDebtMemberwtm:Ark2021SubordinatedNotesTranche1Member2021-07-130000776867wtm:EuroInterbankOfferedRateEURIBORMemberus-gaap:SubordinatedDebtMemberwtm:Ark2021SubordinatedNotesTranche1Member2021-07-012021-07-310000776867us-gaap:SubordinatedDebtMemberwtm:Ark2021SubordinatedNotesTranche2Member2021-08-110000776867wtm:LondonInterbankOfferedRateLIBOR1Memberus-gaap:SubordinatedDebtMemberwtm:Ark2021SubordinatedNotesTranche2Member2021-08-012021-08-310000776867us-gaap:SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMemberus-gaap:SecuredDebtMemberwtm:KuduCreditFacilityMember2023-07-012023-12-310000776867wtm:Ark2021SubordinatedNotesTranche3Memberus-gaap:SubordinatedDebtMember2021-09-080000776867wtm:LondonInterbankOfferedRateLIBOR1Memberwtm:Ark2021SubordinatedNotesTranche3Memberus-gaap:SubordinatedDebtMember2021-09-082021-09-080000776867wtm:Ark2021SubordinatedNotesTranche3Memberus-gaap:SubordinatedDebtMember2024-01-012024-03-310000776867wtm:Ark2021SubordinatedNotesTranche3Memberus-gaap:SubordinatedDebtMember2021-09-012021-09-300000776867us-gaap:LineOfCreditMemberus-gaap:LetterOfCreditMemberwtm:INGLOCFacilityMember2021-12-310000776867us-gaap:LineOfCreditMemberus-gaap:LetterOfCreditMemberwtm:CitibankLOCFacilityMember2021-12-310000776867us-gaap:LineOfCreditMemberus-gaap:LetterOfCreditMemberwtm:LloydsLOCFacilityMember2022-09-300000776867us-gaap:LineOfCreditMemberus-gaap:LetterOfCreditMemberwtm:CitibankLOCFacilityMember2024-03-310000776867us-gaap:LineOfCreditMemberus-gaap:LetterOfCreditMemberwtm:LloydsLOCFacilityMember2024-03-310000776867wtm:HGGlobalSeniorNotesMemberus-gaap:SeniorNotesMember2022-04-290000776867us-gaap:SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMemberwtm:HGGlobalSeniorNotesMemberus-gaap:SeniorNotesMember2022-04-292022-04-290000776867wtm:HGGlobalSeniorNotesMemberus-gaap:SeniorNotesMember2022-04-292022-04-290000776867wtm:HGGlobalSeniorNotesMemberus-gaap:SeniorNotesMember2022-04-300000776867wtm:SubsidiaryHGGlobalMemberus-gaap:InterestRateCapMember2022-06-160000776867wtm:HGGlobalSeniorNotesMemberus-gaap:SeniorNotesMember2022-06-160000776867wtm:HGGlobalSeniorNotesMemberus-gaap:SeniorNotesMember2024-01-012024-03-310000776867wtm:LondonInterbankOfferedRateLIBOR1Memberus-gaap:SecuredDebtMemberwtm:KuduCreditFacilityMember2023-01-012023-06-300000776867us-gaap:SecuredDebtMemberwtm:KuduCreditFacilityMember2023-06-300000776867us-gaap:SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMemberus-gaap:SecuredDebtMemberwtm:KuduCreditFacilityMember2023-07-012023-07-010000776867us-gaap:SecuredDebtMemberwtm:KuduCreditFacilityMember2023-07-010000776867wtm:DebtCovenantPeriod1Memberus-gaap:SecuredDebtMemberwtm:KuduCreditFacilityMember2024-03-310000776867wtm:DebtCovenantPeriod2Memberus-gaap:SecuredDebtMemberwtm:KuduCreditFacilityMember2024-03-310000776867us-gaap:SecuredDebtMemberwtm:DebtCovenantPeriod3Memberwtm:KuduCreditFacilityMember2024-03-310000776867wtm:DebtCovenantPeriod4Memberus-gaap:SecuredDebtMemberwtm:KuduCreditFacilityMember2024-03-310000776867wtm:DebtCovenantPeriod5Memberus-gaap:SecuredDebtMemberwtm:KuduCreditFacilityMember2024-03-310000776867us-gaap:SecuredDebtMemberwtm:KuduCreditFacilityMember2022-12-310000776867us-gaap:SecuredDebtMemberwtm:KuduCreditFacilityMember2024-01-012024-03-310000776867us-gaap:SecuredDebtMemberwtm:KuduCreditFacilityMember2023-01-012023-03-310000776867us-gaap:SecuredDebtMemberwtm:KuduCreditFacilityMember2023-03-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberwtm:ArkInsuranceHoldingsLimitedSegmentMember2024-01-012024-03-310000776867wtm:HGGlobalBAMSegmentMemberwtm:HGGlobalSegmentMember2024-01-012024-03-310000776867us-gaap:SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMemberwtm:SubsidiaryHGGlobalMemberus-gaap:InterestRateCapMember2024-03-310000776867wtm:SubsidiaryHGGlobalMemberus-gaap:InterestRateCapMemberus-gaap:InterestExpenseMember2024-01-012024-03-310000776867wtm:SubsidiaryHGGlobalMemberus-gaap:InterestRateCapMemberus-gaap:InterestExpenseMember2023-01-012023-03-310000776867wtm:SubsidiaryHGGlobalMemberus-gaap:InterestRateCapMember2024-01-012024-03-310000776867wtm:SubsidiaryHGGlobalMemberus-gaap:InterestRateCapMember2023-01-012023-03-310000776867wtm:SubsidiaryHGGlobalMemberus-gaap:InterestRateCapMember2024-03-310000776867wtm:SubsidiaryHGGlobalMemberus-gaap:InterestRateCapMember2023-12-310000776867wtm:SubsidiaryHGGlobalMember2024-03-310000776867wtm:FidusReLtd.Memberwtm:VariableInterestEntityPrimaryBeneficiaryBuildAmericaMutualAssuranceCompanyMember2018-01-012018-12-310000776867wtm:FidusReLtd.Membersrt:MinimumMember2018-01-012018-12-310000776867wtm:FidusReLtd.Membersrt:MaximumMember2018-01-012018-12-310000776867wtm:FidusReLtd.Memberwtm:VariableInterestEntityPrimaryBeneficiaryBuildAmericaMutualAssuranceCompanyMemberwtm:A2018CoveredPortfolioMember2024-01-012024-03-310000776867wtm:FidusReLtd.Memberwtm:VariableInterestEntityPrimaryBeneficiaryBuildAmericaMutualAssuranceCompanyMember2021-01-012021-12-310000776867wtm:FidusReLtd.Membersrt:MinimumMember2021-01-012021-12-310000776867wtm:FidusReLtd.Membersrt:MaximumMember2021-01-012021-12-310000776867wtm:FidusReLtd.Memberwtm:A2021CoveredPortfolioMemberwtm:VariableInterestEntityPrimaryBeneficiaryBuildAmericaMutualAssuranceCompanyMember2024-01-012024-03-310000776867wtm:FidusReLtd.Memberwtm:VariableInterestEntityPrimaryBeneficiaryBuildAmericaMutualAssuranceCompanyMember2022-01-012022-12-310000776867wtm:FidusReLtd.Membersrt:MinimumMember2022-01-012022-12-310000776867wtm:FidusReLtd.Membersrt:MaximumMember2022-01-012022-12-310000776867wtm:FidusReLtd.Memberwtm:A2022CoveredPortfolioMemberwtm:VariableInterestEntityPrimaryBeneficiaryBuildAmericaMutualAssuranceCompanyMember2024-01-012024-03-310000776867wtm:FidusReLtd.Memberwtm:VariableInterestEntityPrimaryBeneficiaryBuildAmericaMutualAssuranceCompanyMember2024-01-012024-03-310000776867wtm:Regulation114Memberwtm:SubsidiaryHGGlobalMember2024-03-310000776867wtm:Regulation114Memberwtm:SubsidiaryHGGlobalMember2023-12-310000776867wtm:SupplementalTrustMemberwtm:SubsidiaryHGGlobalMember2024-03-310000776867wtm:SupplementalTrustMemberwtm:SubsidiaryHGGlobalMember2023-12-310000776867wtm:BAMSurplusNotesMemberwtm:SurplusNotesMemberus-gaap:UsTreasuryUstInterestRateMember2024-01-012024-03-310000776867wtm:BAMSurplusNotesMembersrt:ScenarioForecastMemberwtm:SurplusNotesMemberus-gaap:UsTreasuryUstInterestRateMember2025-01-010000776867wtm:BAMSurplusNotesMembersrt:ScenarioForecastMemberwtm:SurplusNotesMemberus-gaap:UsTreasuryUstInterestRateMember2024-12-310000776867wtm:BAMSurplusNotesMemberwtm:SurplusNotesMember2023-12-012023-12-310000776867wtm:BAMSurplusNotesMemberwtm:SurplusNotesMember2023-12-310000776867wtm:BAMSurplusNotesMemberwtm:SurplusNotesMember2023-01-012023-03-310000776867wtm:BAMSurplusNotesMemberwtm:SurplusNotesMember2024-01-012024-03-310000776867wtm:BAMSurplusNotesMemberwtm:SurplusNotesMember2024-03-310000776867wtm:BuildAmericaMutualAssuranceCompanyMember2024-03-310000776867wtm:BuildAmericaMutualAssuranceCompanyMember2023-12-310000776867wtm:BuildAmericaMutualAssuranceCompanyMember2024-01-012024-03-310000776867wtm:BuildAmericaMutualAssuranceCompanyMember2023-01-012023-12-310000776867wtm:VariableInterestEntityPrimaryBeneficiaryBuildAmericaMutualAssuranceCompanyMember2024-03-310000776867wtm:HGGlobalBAMSegmentMember2024-01-012024-03-310000776867wtm:HGGlobalBAMSegmentMember2023-01-012023-03-310000776867us-gaap:PerformanceSharesMember2024-01-012024-03-310000776867us-gaap:PerformanceSharesMembersrt:MinimumMember2024-01-012024-03-310000776867us-gaap:PerformanceSharesMembersrt:MaximumMember2024-01-012024-03-310000776867us-gaap:PerformanceSharesMember2024-03-012024-03-310000776867us-gaap:PerformanceSharesMember2023-03-012023-03-310000776867us-gaap:PerformanceSharesMember2021-01-012023-12-310000776867us-gaap:PerformanceSharesMember2024-03-310000776867wtm:PerformancePeriodOneMember2024-03-310000776867wtm:PerformancePeriodTwoMember2024-03-310000776867wtm:PerformancePeriodThreeMember2024-03-310000776867us-gaap:RestrictedStockMember2024-01-012024-03-310000776867us-gaap:RestrictedStockMember2023-12-310000776867us-gaap:RestrictedStockMember2022-12-310000776867us-gaap:RestrictedStockMember2023-01-012023-03-310000776867us-gaap:RestrictedStockMember2024-03-310000776867us-gaap:RestrictedStockMember2023-03-310000776867wtm:SubsidiaryArkInsuranceHoldingsLimitedMember2024-03-310000776867wtm:SubsidiaryArkInsuranceHoldingsLimitedMember2023-12-310000776867wtm:SubsidiaryHGGlobalMember2024-03-310000776867wtm:SubsidiaryHGGlobalMember2023-12-310000776867wtm:SubsidiaryHGGlobalMember2023-12-310000776867wtm:SubsidiaryKuduInvestmentManagementLLCMember2024-03-310000776867wtm:SubsidiaryKuduInvestmentManagementLLCMember2023-12-310000776867wtm:SubsidiaryBambooIde8InsuranceServicesLLCMember2024-03-310000776867wtm:SubsidiaryBambooIde8InsuranceServicesLLCMember2023-12-310000776867wtm:OtherNoncontrollingInterestMember2024-03-310000776867wtm:OtherNoncontrollingInterestMember2023-12-310000776867srt:ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember2024-03-310000776867srt:ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember2023-12-310000776867wtm:BuildAmericaMutualAssuranceCompanyMember2024-03-310000776867us-gaap:VariableInterestEntityPrimaryBeneficiaryMember2024-03-310000776867wtm:BuildAmericaMutualAssuranceCompanyMember2023-12-310000776867us-gaap:VariableInterestEntityPrimaryBeneficiaryMember2023-12-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberwtm:ArkInsuranceHoldingsLimitedSegmentMemberus-gaap:OperatingSegmentsMember2024-01-012024-03-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberwtm:WMOutriggerReSegmentMemberus-gaap:OperatingSegmentsMember2024-01-012024-03-310000776867wtm:HGGlobalBAMSegmentMemberwtm:HGGlobalSegmentMemberus-gaap:OperatingSegmentsMember2024-01-012024-03-310000776867wtm:HGGlobalBAMSegmentMemberwtm:BAMSegmentMemberus-gaap:OperatingSegmentsMember2024-01-012024-03-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberwtm:InvestmentsExcludingMediaAlphaMemberwtm:ArkInsuranceHoldingsLimitedSegmentMemberus-gaap:OperatingSegmentsMember2024-01-012024-03-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberwtm:InvestmentsExcludingMediaAlphaMemberwtm:WMOutriggerReSegmentMemberus-gaap:OperatingSegmentsMember2024-01-012024-03-310000776867wtm:InvestmentsExcludingMediaAlphaMemberwtm:HGGlobalBAMSegmentMemberwtm:HGGlobalSegmentMemberus-gaap:OperatingSegmentsMember2024-01-012024-03-310000776867wtm:InvestmentsExcludingMediaAlphaMemberwtm:HGGlobalBAMSegmentMemberwtm:BAMSegmentMemberus-gaap:OperatingSegmentsMember2024-01-012024-03-310000776867wtm:KuduInvestmentManagementLLCSegmentMemberwtm:InvestmentsExcludingMediaAlphaMemberus-gaap:OperatingSegmentsMember2024-01-012024-03-310000776867wtm:BambooIde8InsuranceServicesLLCSegmentMemberwtm:InvestmentsExcludingMediaAlphaMemberus-gaap:OperatingSegmentsMember2024-01-012024-03-310000776867wtm:InvestmentsExcludingMediaAlphaMember2024-01-012024-03-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberwtm:MediaAlphaMemberwtm:ArkInsuranceHoldingsLimitedSegmentMemberus-gaap:OperatingSegmentsMember2024-01-012024-03-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberwtm:MediaAlphaMemberwtm:WMOutriggerReSegmentMemberus-gaap:OperatingSegmentsMember2024-01-012024-03-310000776867wtm:MediaAlphaMemberwtm:HGGlobalBAMSegmentMemberwtm:HGGlobalSegmentMemberus-gaap:OperatingSegmentsMember2024-01-012024-03-310000776867wtm:MediaAlphaMemberwtm:HGGlobalBAMSegmentMemberwtm:BAMSegmentMemberus-gaap:OperatingSegmentsMember2024-01-012024-03-310000776867wtm:KuduInvestmentManagementLLCSegmentMemberwtm:MediaAlphaMemberus-gaap:OperatingSegmentsMember2024-01-012024-03-310000776867wtm:BambooIde8InsuranceServicesLLCSegmentMemberwtm:MediaAlphaMemberus-gaap:OperatingSegmentsMember2024-01-012024-03-310000776867wtm:BambooIde8ServicesLLCSegmentNetOfReconcilingItemsMemberus-gaap:OperatingSegmentsMember2024-01-012024-03-310000776867country:GBwtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberwtm:ArkInsuranceHoldingsLimitedSegmentMember2024-01-012024-03-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberwtm:ArkInsuranceHoldingsLimitedSegmentMembercountry:BM2024-01-012024-03-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberwtm:ArkInsuranceHoldingsLimitedSegmentMemberus-gaap:OperatingSegmentsMember2023-01-012023-03-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberwtm:WMOutriggerReSegmentMemberus-gaap:OperatingSegmentsMember2023-01-012023-03-310000776867wtm:HGGlobalBAMSegmentMemberwtm:HGGlobalSegmentMemberus-gaap:OperatingSegmentsMember2023-01-012023-03-310000776867wtm:HGGlobalBAMSegmentMemberwtm:BAMSegmentMemberus-gaap:OperatingSegmentsMember2023-01-012023-03-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberwtm:InvestmentsExcludingMediaAlphaMemberwtm:ArkInsuranceHoldingsLimitedSegmentMemberus-gaap:OperatingSegmentsMember2023-01-012023-03-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberwtm:InvestmentsExcludingMediaAlphaMemberwtm:WMOutriggerReSegmentMemberus-gaap:OperatingSegmentsMember2023-01-012023-03-310000776867wtm:InvestmentsExcludingMediaAlphaMemberwtm:HGGlobalBAMSegmentMemberwtm:HGGlobalSegmentMemberus-gaap:OperatingSegmentsMember2023-01-012023-03-310000776867wtm:InvestmentsExcludingMediaAlphaMemberwtm:HGGlobalBAMSegmentMemberwtm:BAMSegmentMemberus-gaap:OperatingSegmentsMember2023-01-012023-03-310000776867wtm:KuduInvestmentManagementLLCSegmentMemberwtm:InvestmentsExcludingMediaAlphaMemberus-gaap:OperatingSegmentsMember2023-01-012023-03-310000776867wtm:InvestmentsExcludingMediaAlphaMember2023-01-012023-03-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberwtm:MediaAlphaMemberwtm:ArkInsuranceHoldingsLimitedSegmentMemberus-gaap:OperatingSegmentsMember2023-01-012023-03-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberwtm:MediaAlphaMemberwtm:WMOutriggerReSegmentMemberus-gaap:OperatingSegmentsMember2023-01-012023-03-310000776867wtm:MediaAlphaMemberwtm:HGGlobalBAMSegmentMemberwtm:HGGlobalSegmentMemberus-gaap:OperatingSegmentsMember2023-01-012023-03-310000776867wtm:MediaAlphaMemberwtm:HGGlobalBAMSegmentMemberwtm:BAMSegmentMemberus-gaap:OperatingSegmentsMember2023-01-012023-03-310000776867wtm:KuduInvestmentManagementLLCSegmentMemberwtm:MediaAlphaMemberus-gaap:OperatingSegmentsMember2023-01-012023-03-310000776867country:GBwtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberwtm:ArkInsuranceHoldingsLimitedSegmentMember2023-01-012023-03-310000776867wtm:ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMemberwtm:ArkInsuranceHoldingsLimitedSegmentMembercountry:BM2023-01-012023-03-310000776867wtm:SubsidiaryBAMMember2024-01-012024-03-310000776867us-gaap:VariableInterestEntityNotPrimaryBeneficiaryMemberwtm:PassportCardDavidShieldMember2024-01-012024-03-310000776867us-gaap:VariableInterestEntityNotPrimaryBeneficiaryMemberwtm:PassportCardDavidShieldMember2024-03-310000776867us-gaap:VariableInterestEntityNotPrimaryBeneficiaryMemberwtm:ElementumHoldingsL.P.Member2024-01-012024-03-310000776867us-gaap:VariableInterestEntityNotPrimaryBeneficiaryMemberwtm:ElementumHoldingsL.P.Member2024-03-310000776867us-gaap:VariableInterestEntityNotPrimaryBeneficiaryMemberwtm:LimitedPartnershipsMember2024-03-310000776867wtm:KuduParticipationContractsMembersrt:MinimumMember2024-03-310000776867wtm:KuduParticipationContractsMembersrt:MaximumMember2024-03-310000776867wtm:KuduParticipationContractsMember2024-03-310000776867wtm:KuduParticipationContractsMembersrt:MinimumMember2023-12-310000776867wtm:KuduParticipationContractsMembersrt:MaximumMember2023-12-310000776867wtm:KuduParticipationContractsMember2023-12-310000776867wtm:PassportCardDavidShieldMember2024-03-310000776867wtm:PassportCardDavidShieldMember2023-12-310000776867wtm:ElementumHoldingsL.P.Member2024-03-310000776867wtm:ElementumHoldingsL.P.Member2023-12-310000776867wtm:EquityMethodEligibleInvestmentsLessThanFiftyPercentMember2024-03-310000776867wtm:EquityMethodEligibleInvestmentsLessThanFiftyPercentMember2023-12-310000776867wtm:EquityMethodEligibleInvestmentsGreaterThanFiftyPercentMember2024-03-310000776867wtm:EquityMethodEligibleInvestmentsGreaterThanFiftyPercentMember2023-12-310000776867wtm:Ark2007SubordinatedNotesMember2024-03-310000776867wtm:Ark2007SubordinatedNotesMember2023-12-310000776867wtm:Ark2021SubordinatedNotesMember2024-03-310000776867wtm:Ark2021SubordinatedNotesMember2023-12-310000776867wtm:HGGlobalSeniorNotesMember2024-03-310000776867wtm:HGGlobalSeniorNotesMember2023-12-31

UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549
 
FORM 10-Q
    QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934
 
For the period ended March 31, 2024
 
OR
 
         TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934
 
For the transition period from          to         
Commission file number 1-8993

WHITE MOUNTAINS INSURANCE GROUP, LTD.
(Exact name of Registrant as specified in its charter)
Bermuda 
(State or other jurisdiction of incorporation or organization) 94-2708455
23 South Main Street, Suite 3B (I.R.S. Employer Identification No.)
Hanover, 03755-2053
New Hampshire(Zip Code)
(Address of principal executive offices) 
 
Registrant’s telephone number, including area code: (603640-2200
 Securities registered pursuant to Section 12(b) of the Act:
Title of each classTrading Symbol(s)Name of each exchange on which registered
Common Shares, par value $1.00 per shareWTMNew York Stock Exchange
WTM.BHBermuda Stock Exchange
Indicate by check mark whether the Registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the Registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. Yes   ý   No   
 
Indicate by check mark whether the Registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the Registrant was required to submit such files). Yes   ý    No   
 
Indicate by check mark whether the Registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company.  See the definitions of “large accelerated filer,” “accelerated filer”, “smaller reporting company” and “emerging growth company” in Rule 12b-2 of the Exchange Act.
Large accelerated filerýAccelerated filerNon-accelerated filer
Smaller reporting companyEmerging growth company

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.  o
 
Indicate by check mark whether the Registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act). Yes     No  ý

As of May 6, 2024, 2,565,733 common shares with a par value of $1.00 per share were outstanding (which includes 34,525 restricted common shares that were not vested at such date).




WHITE MOUNTAINS INSURANCE GROUP, LTD.

Table of Contents
 
  Page No.
   
 
   
 
   
 
Consolidated Balance Sheets, March 31, 2024 and December 31, 2023
  
 
 
     Three Months Ended March 31, 2024 and 2023
 
Consolidated Statements of Changes in Equity, Three Months Ended March 31, 2024 and 2023
 
Consolidated Statements of Cash Flows, Three Months Ended March 31, 2024 and 2023
  
 
  
  
 
Results of Operations for the Three Months Ended March 31, 2024 and 2023
  
 
  
 
 
  
 
  
  
  
  
  





Part I.FINANCIAL INFORMATION.
Item 1.Financial Statements
WHITE MOUNTAINS INSURANCE GROUP, LTD.
CONSOLIDATED BALANCE SHEETS
(Unaudited)
Millions, except share and per share amountsMarch 31, 2024December 31, 2023
Assets
P&C Insurance and Reinsurance (Ark/WM Outrigger)
Fixed maturity investments, at fair value$946.9 $866.8 
Common equity securities, at fair value409.9 400.6 
Short-term investments, at fair value835.3 962.8 
Other long-term investments485.0 440.9 
Total investments2,677.1 2,671.1 
Cash (restricted $24.7 and $0.7)
129.1 90.5 
Reinsurance recoverables695.0 442.0 
Insurance premiums receivable1,001.5 612.2 
Deferred acquisition costs213.3 145.3 
Goodwill and other intangible assets292.5 292.5 
Other assets140.9 125.0 
Total P&C Insurance and Reinsurance assets5,149.4 4,378.6 
Financial Guarantee (HG Global/BAM)
Fixed maturity investments, at fair value1,015.7 1,012.3 
Short-term investments, at fair value54.7 70.6 
Total investments1,070.4 1,082.9 
Cash4.7 6.7 
Insurance premiums receivable5.8 5.5 
Deferred acquisition costs40.9 40.1 
Other assets36.8 36.8 
Total Financial Guarantee assets1,158.6 1,172.0 
Asset Management (Kudu)
     Short-term investments, at fair value19.8 29.3 
     Other long-term investments889.9 896.3 
Total investments909.7 925.6 
     Cash6.5 1.4 
     Accrued investment income22.1 17.6 
     Goodwill and other intangible assets8.2 8.3 
     Other assets6.6 6.5 
Total Asset Management assets953.1 959.4 
P&C Insurance Distribution (Bamboo)
Fixed maturity investments, at fair value24.6  
Short-term investments, at fair value18.6  
Total investments43.2  
Cash (restricted $58.3 and $0.0)
62.0  
Premiums, commissions and fees receivable43.3  
Goodwill and other intangible assets367.2  
Other assets12.4  
Total P&C Insurance Distribution assets528.1  
Other Operations
     Fixed maturity investments, at fair value267.4 230.2 
     Common equity securities, at fair value151.6 137.8 
Investment in MediaAlpha, at fair value465.6 254.9 
     Short-term investments, at fair value126.1 425.2 
     Other long-term investments617.0 661.0 
     Total investments1,627.7 1,709.1 
     Cash23.0 23.8 
     Goodwill and other intangible assets68.7 69.8 
     Other assets81.7 73.2 
     Total Other Operations assets1,801.1 1,875.9 
Total assets$9,590.3 $8,385.9 
See Notes to Consolidated Financial Statements
1



CONSOLIDATED BALANCE SHEETS (CONTINUED)
(Unaudited)
Millions, except share and per share amountsMarch 31, 2024December 31, 2023
Liabilities
P&C Insurance and Reinsurance (Ark/WM Outrigger)
Loss and loss adjustment expense reserves$1,744.5 $1,605.1 
Unearned insurance premiums1,234.7 743.6 
Debt155.4 185.5 
Reinsurance payable262.5 81.1 
Contingent consideration94.0 94.0 
Other liabilities190.1 166.8 
Total P&C Insurance and Reinsurance liabilities3,681.2 2,876.1 
Financial Guarantee (HG Global/BAM)
Unearned insurance premiums328.5 325.8 
Debt147.0 146.9 
Accrued incentive compensation11.9 27.2 
Other liabilities31.9 31.8 
Total Financial Guarantee liabilities519.3 531.7 
Asset Management (Kudu)
Debt203.8 203.8 
Other liabilities61.8 71.6 
Total Asset Management liabilities265.6 275.4 
P&C Insurance Distribution (Bamboo)
Loss and loss adjustment expense reserves12.3  
Unearned insurance premiums25.7  
Premiums and commissions payable61.7  
Other liabilities18.6  
Total P&C Insurance Distribution liabilities118.3  
Other Operations
Debt25.9 28.4 
Accrued incentive compensation47.6 87.7 
Other liabilities41.8 25.0 
Total Other Operations liabilities115.3 141.1 
Total liabilities4,699.7 3,824.3 
Equity
White Mountains’s common shareholders’ equity
White Mountains’s common shares at $1 par value per share—authorized 50,000,000
   shares; issued and outstanding 2,565,733 and 2,560,452 shares
2.6 2.6 
Paid-in surplus551.9548.7
Retained earnings3,917.7 3,690.8 
Accumulated other comprehensive income (loss), after-tax:
Net unrealized gains (losses) from foreign currency translation(1.8)(1.6)
Total White Mountains’s common shareholders’ equity4,470.4 4,240.5 
Noncontrolling interests420.2 321.1 
Total equity4,890.6 4,561.6 
Total liabilities and equity$9,590.3 $8,385.9 
See Notes to Consolidated Financial Statements

2


WHITE MOUNTAINS INSURANCE GROUP, LTD.
CONSOLIDATED STATEMENTS OF OPERATIONS
(Unaudited)

Three Months Ended March 31,
Millions20242023
Revenues:
P&C Insurance and Reinsurance (Ark/WM Outrigger)
Earned insurance premiums$302.8 $255.1 
Net investment income19.9 10.6 
Net realized and unrealized investment gains (losses)10.6 24.5 
Other revenues3.5 (2.7)
Total P&C Insurance and Reinsurance revenues336.8 287.5 
Financial Guarantee (HG Global/BAM)
Earned insurance premiums7.8 7.7 
Net investment income9.7 7.2 
Net realized and unrealized investment gains (losses)(10.1)17.0 
Other revenues.5 .8 
Total Financial Guarantee revenues7.9 32.7 
Asset Management (Kudu)
Net investment income17.2 14.2 
Net realized and unrealized investment gains (losses)(6.5)29.6 
Total Asset Management revenues10.7 43.8 
P&C Insurance Distribution (Bamboo)
Commission and fee revenues21.9  
Earned insurance premiums8.4  
Other revenues.8  
Total P&C Insurance Distribution revenues31.1  
Other Operations
   Net investment income9.9 7.0 
   Net realized and unrealized investment gains (losses)22.2 41.8 
   Net realized and unrealized investment gains (losses) from investment in MediaAlpha 210.7 85.2 
   Commission revenues3.6 3.3 
   Other revenues14.4 30.6 
Total Other Operations revenues260.8 167.9 
Total revenues$647.3 $531.9 
See Notes to Consolidated Financial Statements
3


CONSOLIDATED STATEMENTS OF OPERATIONS (CONTINUED)
(Unaudited)

Three Months Ended March 31,
Millions20242023
Expenses:
P&C Insurance and Reinsurance (Ark/WM Outrigger)
Loss and loss adjustment expenses$180.0 $147.8 
Acquisition expenses66.3 59.8 
General and administrative expenses42.2 35.2 
Change in fair value of contingent consideration (2.4)
Interest expense5.4 5.0 
Total P&C Insurance and Reinsurance expenses293.9 245.4 
Financial Guarantee (HG Global/BAM)
Acquisition expenses2.2 2.7 
General and administrative expenses17.3 17.3 
Interest expense3.5 4.5 
Total Financial Guarantee expenses23.0 24.5 
Asset Management (Kudu)
General and administrative expenses3.4 3.8 
Interest expense5.6 4.7 
Total Asset Management expenses9.0 8.5 
P&C Insurance Distribution (Bamboo)
Broker commission expenses9.3  
Loss and loss adjustment expenses5.8  
Acquisition expenses3.1  
General and administrative expenses12.0  
Total P&C Insurance Distribution expenses30.2  
Other Operations
   Cost of sales7.6 13.9 
   General and administrative expenses50.3 39.7 
   Interest expense.7 .8 
Total Other Operations expenses58.6 54.4 
Total expenses414.7 332.8 
Pre-tax income (loss)232.6 199.1 
   Income tax (expense) benefit(10.8)(11.9)
Net income (loss)221.8 187.2 
   Net (income) loss attributable to noncontrolling interests14.6 (7.7)
Net income (loss) attributable to White Mountains’s common shareholders$236.4 $179.5 
See Notes to Consolidated Financial Statements
4


WHITE MOUNTAINS INSURANCE GROUP, LTD.
CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME
(Unaudited)

Three Months Ended March 31,
Millions20242023
Net income (loss) attributable to White Mountains’s common shareholders$236.4 $179.5 
Other comprehensive income, net of tax:
Other comprehensive income (loss), net of tax(.3)1.2 
Comprehensive income (loss) 236.1 180.7 
Other comprehensive (income) loss attributable to noncontrolling interests.1 (.4)
Comprehensive income (loss) attributable to White Mountains’s common shareholders$236.2 $180.3 

Earnings (loss) per share attributable to White Mountains’s common shareholders:
Basic earnings (loss) per share
Continuing operations$92.33 $69.83 
Discontinued operations  
Total consolidated operations$92.33 $69.83 
Diluted earnings (loss) per share
Continuing operations$92.33 $69.83 
Discontinued operations  
Total consolidated operations$92.33 $69.83 
Dividends declared and paid per White Mountains’s common share$1.00 $1.00 
See Notes to Consolidated Financial Statements.

5


WHITE MOUNTAINS INSURANCE GROUP, LTD.
CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY
(Unaudited)

 White Mountains’s Common Shareholders’ Equity 
MillionsCommon shares and paid-in surplusRetained earningsAOCI, after taxTotalNon-controlling interestTotal Equity
Balance as of January 1, 2024$551.3 $3,690.8 $(1.6)$4,240.5 $321.1 $4,561.6 
Net income (loss) 236.4  236.4 (14.6)221.8 
Other comprehensive income (loss), net of tax  (.2)(.2)(.1)(.3)
Total comprehensive income (loss) 236.4 (.2)236.2 (14.7)221.5 
Dividends declared on common shares (2.5) (2.5) (2.5)
Dividends to noncontrolling interests    (9.8)(9.8)
Issuances of common shares.3   .3  .3 
Repurchases and retirements of common shares(1.1)(7.0) (8.1) (8.1)
BAM member surplus contributions, net of tax    11.4 11.4 
Amortization of restricted share awards3.2   3.2  3.2 
Recognition of equity-based compensation expense
   of subsidiaries
.6   .6 .2 .8 
Net contributions (distributions) and dilution from
   other noncontrolling interests
.2   .2 .9 1.1 
Acquisition of noncontrolling interests - Bamboo    111.1 111.1 
Balance as of March 31, 2024$554.5 $3,917.7 $(1.8)$4,470.4 $420.2 $4,890.6 

 White Mountains’s Common Shareholders’ Equity 
MillionsCommon shares and paid-in surplusRetained earningsAOCI, after taxTotalNon-controlling interestTotal Equity
Balance as of January 1, 2023$538.6 $3,211.8 $(3.5)$3,746.9 $188.1 $3,935.0 
Net income (loss)— 179.5 — 179.5 7.7 187.2 
Other comprehensive income (loss), net of tax— — .8 .8 .4 1.2 
Total comprehensive income (loss)— 179.5 .8 180.3 8.1 188.4 
Dividends declared on common shares— (2.6)— (2.6)— (2.6)
Dividends to noncontrolling interests— — — — (7.2)(7.2)
Issuances of common shares.1 — — .1 — .1 
Repurchases and retirements of common shares(3.9)(21.4)— (25.3)— (25.3)
BAM member surplus contributions, net of tax— — — — 11.8 11.8 
Amortization of restricted share awards3.1 — — 3.1 — 3.1 
Recognition of equity-based compensation expense
   of subsidiaries
.4 — — .4 .2 .6 
Net contributions and dilution from other
   noncontrolling interests
(.5)— — (.5)(1.2)(1.7)
Disposition of noncontrolling interests— — — — (9.4)(9.4)
Balance as of March 31, 2023$537.8 $3,367.3 $(2.7)$3,902.4 $190.4 $4,092.8 
See Notes to Consolidated Financial Statements.
6



WHITE MOUNTAINS INSURANCE GROUP, LTD.
CONSOLIDATED STATEMENTS OF CASH FLOWS
(Unaudited)
Three Months Ended March 31,
Millions20242023
Cash flows from operations:
Net income (loss)$221.8 $187.2 
Adjustments to reconcile net income to net cash provided from (used for) operations:  
Net realized and unrealized investment (gains) losses(16.2)(112.9)
Net realized and unrealized investment (gains) losses from investment in MediaAlpha(210.7)(85.2)
Deferred income tax expense (benefit)(9.8)(3.6)
Amortization of restricted share awards3.2 3.1 
Amortization (accretion) and depreciation(2.1)(2.4)
Change in fair value of contingent consideration - Ark (2.4)
Other operating items: 
Net change in reinsurance recoverables(253.0)24.7 
Net change in insurance premiums, commissions and fees receivable(394.9)(365.3)
Net change in deferred acquisition costs(68.8)(82.2)
Net change in loss and loss adjustment expense reserves142.4 49.1 
Net change in unearned insurance premiums499.4 501.8 
Net change in reinsurance payable181.4 (58.1)
Net change in premiums and commissions payable12.5  
Contributions to Kudu’s Participation Contracts (30.9)
Proceeds from Kudu’s Participation Contracts sold 62.9 
Net other operating activities(68.7)(.2)
Net cash provided from (used for) operations36.5 85.6 
Cash flows from investing activities:  
Net change in short-term investments441.3 47.6 
Sales of fixed maturity investments185.8 54.6 
Maturities, calls and paydowns of fixed maturity investments81.8 66.8 
Distributions and redemptions of other long-term investments91.5 2.0 
Proceeds from the sale of Other Operating Businesses, net of cash sold of $0.0 and $0.8
 17.3 
Purchases of consolidated subsidiaries, net of cash acquired of $44.9 and $0.0
(231.8) 
Purchases of fixed maturity investments(417.3)(127.6)
Purchases of other long-term investments(79.9)(146.1)
Net other investing activities29.2 (11.2)
Net cash provided from (used for) investing activities100.6 (96.6)
Cash flows from financing activities:  
Repayment of debt and revolving lines of credit(32.6)(20.0)
Cash dividends paid to common shareholders(2.5)(2.6)
Repurchases and retirements of common shares(8.1)(25.3)
BAM member surplus contributions11.4 11.8 
Net contributions from (distributions to) other noncontrolling interests1.1 (1.7)
Fidus Re premium payments(3.5)(3.5)
Net cash provided from (used for) financing activities(34.2)(41.3)
Net change in cash during the period102.9 (52.3)
Cash balances at beginning of period (includes restricted cash balances of $0.7 and $12.2)
122.4 255.0 
Cash balances at end of period (includes restricted cash balances of $83.0 and $13.0)
$225.3 $202.7 
Supplemental cash flows information: 
Interest paid$(16.7)$(5.8)
Net income tax payments(5.3)(17.8)
See Notes to Consolidated Financial Statements
7


NOTES TO CONSOLIDATED FINANCIAL STATEMENTS (Unaudited)

Note 1. Basis of Presentation and Significant Accounting Policies

Basis of Presentation

White Mountains Insurance Group, Ltd. (the “Company” or the “Registrant”) is an exempted Bermuda limited liability company whose principal businesses are conducted through its subsidiaries and other affiliates. The Company’s headquarters is located at 26 Reid Street, Hamilton, Bermuda HM 11, its principal executive office is located at 23 South Main Street, Suite 3B, Hanover, New Hampshire 03755-2053 and its registered office is located at Clarendon House, 2 Church Street, Hamilton, Bermuda HM 11. The Company’s website is www.whitemountains.com. The information contained on White Mountains’s website is not incorporated by reference into, and is not a part of, this report.
The accompanying consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States (“GAAP”) and include the accounts of the Company, its subsidiaries (collectively with the Company, “White Mountains”) and other entities required to be consolidated under GAAP. Intercompany transactions have been eliminated in consolidation. Certain amounts in the prior period financial statements have been reclassified to conform to the current presentation.
The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.
These interim financial statements include all adjustments considered necessary by management to fairly state the financial position, results of operations and cash flows of White Mountains. These interim financial statements may not be indicative of financial results for the full year and should be read in conjunction with the Company’s 2023 Annual Report on Form 10-K.

Reportable Segments
As of March 31, 2024, White Mountains conducted its operations through four reportable segments: (1) Ark/WM Outrigger, (2) HG Global/BAM, (3) Kudu and (4) Bamboo, with our remaining operating businesses, holding companies and other assets included in Other Operations. White Mountains has made its segment determination based on consideration of the following criteria: (i) the nature of the business activities of each of the Company’s subsidiaries and affiliates; (ii) the manner in which the Company’s subsidiaries and affiliates are organized; (iii) the existence of primary managers responsible for specific subsidiaries and affiliates; and (iv) the organization of information provided to the Company’s chief operating decision makers and its Board of Directors. See Note 14 — “Segment Information.”
The Ark/WM Outrigger segment consists of Ark Insurance Holdings Limited and its subsidiaries (collectively, “Ark”) and Outrigger Re Ltd. Segregated Account 2023-1 (“WM Outrigger Re”) (collectively with Ark, “Ark/WM Outrigger”). Ark is a specialty property and casualty insurance and reinsurance company that offers a wide range of niche insurance and reinsurance products, including property, specialty, marine & energy, accident & health and casualty. Ark underwrites select coverages through Lloyd’s Syndicates 4020 and 3902 (the “Syndicates”) and its wholly-owned subsidiary Group Ark Insurance Limited (“GAIL”). White Mountains acquired a controlling ownership interest in Ark on January 1, 2021 (the “Ark Transaction”). As of March 31, 2024 and December 31, 2023, White Mountains owned 72.0% of Ark on a basic shares outstanding basis (61.9% after taking account of management’s equity incentives). The remaining shares are owned by current and former employees of Ark. In the future, management rollover shareholders could earn additional shares in Ark if and to the extent that White Mountains achieves certain thresholds for its multiple of invested capital return. If fully earned, these additional shares would represent 12.5% of the shares outstanding at closing. The liability related to these additional shares is recorded as contingent consideration. During the fourth quarter of 2022, Ark sponsored the formation of Outrigger Re Ltd., a Bermuda company registered as a special purpose insurer and segregated accounts company, to provide reinsurance capacity to Ark. White Mountains consolidates the results of its segregated account, WM Outrigger Re, in its financial statements. See Note 2 — “Significant Transactions.” As of March 31, 2024 and December 31, 2023, White Mountains owned 100.0% of WM Outrigger Re’s preferred equity.
8


The HG Global/BAM segment consists of HG Global Ltd. and its wholly-owned subsidiaries (collectively, “HG Global”) and the consolidated results of Build America Mutual Assurance Company (“BAM”) (collectively with HG Global, “HG Global/BAM”). BAM is the first and only mutual municipal bond insurance company in the United States. By insuring the timely payment of principal and interest, BAM provides market access to, and lowers interest expense for, issuers of municipal bonds used to finance essential public purpose projects, such as schools, utilities and transportation facilities. BAM is owned by and operated for the benefit of its members, the municipalities whose debt issuances are insured by BAM. HG Global was established to fund the startup of BAM and, through its reinsurance subsidiary, HG Re Ltd. (“HG Re”), to provide up to 15%-of-par, first loss reinsurance protection for policies underwritten by BAM. HG Global, together with its subsidiaries, funded the initial capitalization of BAM through the purchase of $503.0 million of surplus notes issued by BAM (the “BAM Surplus Notes”). As of March 31, 2024 and December 31, 2023, White Mountains owned 96.9% of HG Global’s preferred equity and 88.4% of its common equity. White Mountains does not have an ownership interest in BAM. However, White Mountains is required to consolidate BAM’s results in its financial statements because BAM is a variable interest entity (“VIE”) for which White Mountains is the primary beneficiary. BAM’s results are all attributed to noncontrolling interests.
The Kudu segment consists of Kudu Investment Management, LLC and its subsidiaries (collectively “Kudu”). Kudu provides capital solutions for boutique asset and wealth managers for a variety of purposes including generational ownership transfers, management buyouts, acquisition and growth finance and legacy partner liquidity. Kudu also provides strategic assistance to investees from time to time. Kudu’s capital solutions generally are structured as minority preferred equity stakes with distribution rights, typically tied to gross revenues and designed to generate immediate cash yields. As of March 31, 2024 and December 31, 2023, White Mountains owned 89.4% and 89.6% of Kudu’s basic units outstanding (76.2% and 76.3% on a fully-diluted, fully-converted basis).
The Bamboo segment consists of PM Holdings LLC (“Bamboo Holdings”), Bamboo Ide8 Insurance Services LLC (“Bamboo MGA”) and Ide8 Limited (“Bamboo Captive”) (collectively with Bamboo Holdings and Bamboo MGA, “Bamboo”). Bamboo is a capital-light, tech- and data-enabled insurance distribution platform providing homeowners’ insurance and related products to the residential property market in California. Bamboo operates primarily through Bamboo MGA, its full-service managing general agent (“MGA”) business, where the company manages all aspects of the placement process on behalf of its fronting and reinsurance partners, including product development, marketing, underwriting, policy issuance and claims oversight, and it earns commissions based on the volume and profitability of the insurance that it places. It offers both admitted and non-admitted products. Bamboo also operates two separate but integrated businesses: (i) a retail agency, within Bamboo MGA, offering ancillary products on behalf of third parties and (ii) Bamboo Captive, a Bermuda-domiciled captive reinsurer that participates in the underwriting risk of Bamboo’s MGA programs to align interests with reinsurance partners. On January 2, 2024, White Mountains acquired a controlling interest in Bamboo. See Note 2 — “Significant Transactions”. As of March 31, 2024, White Mountains owned 72.8% of the basic units outstanding of Bamboo (63.7% on a fully-diluted, fully-converted basis).
White Mountains’s other operations consist of the Company and its wholly-owned subsidiary, White Mountains Capital, LLC (“WM Capital”), its other intermediate holding companies, its wholly-owned investment management subsidiary, White Mountains Advisors LLC (“WM Advisors”), investment assets managed by WM Advisors, its interests in MediaAlpha, Inc. (“MediaAlpha”), PassportCard Limited (“PassportCard”) and DavidShield Life Insurance Agency (2000) Ltd. (“DavidShield”) (collectively, “PassportCard/DavidShield”), Elementum Holdings LP (“Elementum”), certain other consolidated and unconsolidated entities (“Other Operating Businesses”) and certain other assets (collectively, “Other Operations”).
On October 25, 2023, White Mountains announced the launch of White Mountains Partners LLC (“WTM Partners”), which will acquire businesses in non-insurance, non-financial services sectors including essential services, light industrial and specialty consumer. White Mountains expects to deploy up to $500.0 million of equity capital through WTM Partners over time. WTM Partners is included within Other Operations.

Significant Accounting Policies

In addition to the following, refer to the Notes to Consolidated Financial Statements in the Company’s 2023 Annual Report on Form 10-K for a complete discussion regarding White Mountains’s significant accounting policies.


9


Revenue Recognition
Bamboo’s revenues consist primarily of commission and fee revenues for placement of insurance policies. Commission and fee revenues are measured based on the contractual rates with insurance carriers, net of any amounts expected to be uncollectible and any amounts associated with expected policy cancellations and adjustments, and are recognized when contractual performance obligations have been fulfilled. Bamboo’s primary contractual performance obligations are generally satisfied upon the issuance of an insurance policy. Where Bamboo has significant performance obligations beyond the policy effective date, Bamboo estimates the relative standalone selling price for the post-issuance services using the price charged for the service when sold separately in similar circumstances to similar customers in order to allocate the transaction price.
Bamboo’s premiums, commissions and fees receivable consist of insurance premiums and fees receivable from customers and commissions receivable from insurance carriers, net of a provision for amounts estimated to be uncollectible and any amounts associated with expected policy cancellations and adjustments.
Deferred revenues associated with unsatisfied performance obligations are recognized within other liabilities.

Broker Commission Expenses
Bamboo’s broker commission expense consists of commissions paid to sub-agents and brokers. Broker commission expense is measured in accordance with contractual terms and recognized when incurred, which is generally at the policy issuance date.

Note 2. Significant Transactions

Bamboo Transaction

On October 19, 2023, White Mountains entered into an agreement and plan of merger (the “Bamboo Merger Agreement”) with Bamboo MGA and John Chu, as the unitholders’ representative. Under the terms of the Bamboo Merger Agreement, White Mountains’s wholly-owned subsidiary, WM Pierce Merger Sub LLC, agreed to merge with and into Bamboo MGA, with Bamboo MGA continuing as the surviving company (the “Bamboo Merger”). Concurrently with the execution of the Bamboo Merger Agreement, certain Bamboo management unitholders agreed to roll over the majority of their existing equity in Bamboo MGA into Bamboo Holdings. White Mountains also agreed to make an equity contribution to Bamboo immediately following the Bamboo Merger (together with the Bamboo Merger and the rollover transactions, the “Bamboo Transaction”).
On January 2, 2024, White Mountains closed the Bamboo Transaction in accordance with the terms of the Bamboo Merger Agreement, investing $296.7 million of equity into Bamboo, which included the contribution of $36.0 million to retire Bamboo’s legacy credit facility and the contribution of $20.0 million of primary capital. The consideration is subject to customary purchase price adjustments. At closing, White Mountains owned 72.8% of Bamboo on a basic shares outstanding basis (63.7% on a fully-diluted/fully-converted basis, taking account of management’s equity incentives), while Bamboo management owned 16.1% of basic shares outstanding (26.6% on a fully-diluted/fully-converted basis).
White Mountains recognized total assets acquired related to the Bamboo Transaction of $479.5 million, total liabilities assumed of $91.7 million and noncontrolling interest of $111.1 million reflecting acquisition date fair values. Total assets acquired included $371.4 million of goodwill and other intangible assets. In connection with the acquisition, White Mountains incurred transaction costs of $4.0 million in Other Operations, of which $0.3 million were expensed in the first quarter of 2024.

10


The following presents additional details of the assets acquired and liabilities assumed as of the January 2, 2024 acquisition date:
MillionsAs of January 2, 2024
Fixed maturity investments, at fair value$8.2
Short-term investments, at fair value9.3
Cash (restricted $37.0)
44.9
(1)
Premiums and commissions receivable38.0
Other assets7.7
   Total tangible assets108.1
Loss and loss adjustment expense reserves(9.3)
Unearned insurance premiums(20.1)
Premiums and commissions payable(49.2)
Other liabilities(13.1)
   Total tangible liabilities(91.7)
Net tangible assets acquired 16.4
Goodwill 270.4
Other intangible assets101.0
   Total goodwill and other intangible assets371.4
Net assets acquired$387.8
(1) Cash excludes the White Mountains cash contribution of $20.0 as part of the Bamboo Transaction,
which is not part of the purchase consideration.

The values of net tangible assets acquired and the resulting goodwill and other intangible assets were recorded at fair value using Level 3 inputs. The majority of the tangible assets acquired and liabilities assumed were recorded at their carrying values, as their carrying values approximated their fair values due to their short-term nature. The fair values of other intangible assets were internally estimated based primarily on the income approach. The income approach estimates fair value based on the present value of the cash flows that the assets are expected to generate in the future. White Mountains developed internal estimates for the expected future cash flows and discount rates used in the present value calculations. See Note 4 — “Goodwill and Other Intangible Assets.”
The value of the noncontrolling interest is recorded at the acquisition date fair value, based on the valuation implied in the Bamboo Transaction.
Bamboo’s segment income and expenses for three months ended March 31, 2024 are presented in Note 14 — “Segment Information.”

WM Outrigger Re

During the fourth quarter of 2022, Ark sponsored the formation of Outrigger Re Ltd., a Bermuda company registered as a special purpose insurer and segregated accounts company, to provide reinsurance capacity to Ark. Outrigger Re Ltd. was capitalized with $250.0 million of preference shares for business written in the 2023 underwriting year, of which White Mountains contributed $205.0 million. The remaining capital was provided by unrelated third-party investors. Outrigger Re Ltd. entered into collateralized quota share agreements with GAIL to provide reinsurance protection on Ark’s Bermuda global property catastrophe excess of loss portfolio written in the 2023 underwriting year. The proceeds from the issuance of the preference shares were deposited into collateral trust accounts to fund any potential obligations under the reinsurance agreements with GAIL. Outrigger Re Ltd.’s obligations under the reinsurance agreements with GAIL are subject to an aggregate limit equal to the assets in the collateral trusts at any point in time. The terms of the reinsurance agreements are renewable upon the mutual agreement of Ark and the applicable preference shareholder of Outrigger Re Ltd.
During the fourth quarter of 2023, Ark renewed Outrigger Re Ltd. for the 2024 underwriting year with $250.0 million of capital, of which White Mountains rolled over $130.0 million from its commitment to the 2023 underwriting year. The remaining capital was provided by new and continuing unrelated third-party investors.
11


As of March 31, 2024 and December 31, 2023, short-term investments of $222.4 million and $265.3 million were held in a collateral trust account required to be maintained in relation to WM Outrigger Re’s reinsurance agreement with GAIL.
White Mountains owns 100% of the preference shares linked to its segregated account, WM Outrigger Re. White Mountains consolidates WM Outrigger Re’s results in its financial statements. WM Outrigger Re’s quota share reinsurance agreement with GAIL eliminates in White Mountains’s consolidated financial statements.
During January 2024, White Mountains received an initial return of capital of $68.1 million from WM Outrigger Re for business written in the 2023 underwriting year. White Mountains expects to receive any additional return of capital and associated profits from business written in the 2023 underwriting year beginning in the third quarter of 2024.

Note 3.  Investment Securities

White Mountains’s portfolio of investment securities held for general investment purposes consists of fixed maturity investments, short-term investments, common equity securities, its investment in MediaAlpha and other long-term investments. White Mountains’s portfolio of fixed maturity investments, including those within short-term investments, are classified as trading securities. Trading securities are reported at fair value as of the balance sheet date. Short-term investments also include interest-bearing money market funds and certificates of deposit that are carried at fair value. White Mountains’s portfolio of common equity securities, its investment in MediaAlpha and other long-term investments are measured at fair value. Other long-term investments consist primarily of unconsolidated entities, Kudu’s Participation Contracts, private equity funds and hedge funds, a bank loan fund, Lloyd’s trust deposits, ILS funds and private debt instruments. White Mountains has taken the fair value option for its equity method eligible investments. See Note 16 — Equity Method Eligible Investments”. Net realized and unrealized investment gains (losses) are reported in pre-tax revenues.

Net Investment Income

White Mountains’s net investment income is comprised primarily of interest income associated with White Mountains’s fixed maturity investments and short-term investments, dividend income from common equity securities and distributions from other long-term investments.
The following table presents pre-tax net investment income for the three months ended March 31, 2024 and 2023: