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SCHEDULE III SUPPLEMENTARY INSURANCE INFORMATION (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
SUPPLEMENTARY INSURANCE INFORMATION |  |  |
Net investment income | $ 105.0 us-gaap_NetInvestmentIncome | $ 110.9 us-gaap_NetInvestmentIncome | $ 153.6 us-gaap_NetInvestmentIncome
OneBeacon |  |  |
SUPPLEMENTARY INSURANCE INFORMATION |  |  |
Deferred acquisition costs | 103.2 us-gaap_SupplementaryInsuranceInformationDeferredPolicyAcquisitionCosts / us-gaap_StatementBusinessSegmentsAxis = wtm_OnebeaconMember | 103.7 us-gaap_SupplementaryInsuranceInformationDeferredPolicyAcquisitionCosts / us-gaap_StatementBusinessSegmentsAxis = wtm_OnebeaconMember | 123.9 us-gaap_SupplementaryInsuranceInformationDeferredPolicyAcquisitionCosts / us-gaap_StatementBusinessSegmentsAxis = wtm_OnebeaconMember
Future policy benefits, losses, claims and loss expenses | 1,342.2 us-gaap_SupplementaryInsuranceInformationLiabilityForFuturePolicyBenefitsLossesClaimsAndLossExpenseReserves / us-gaap_StatementBusinessSegmentsAxis = wtm_OnebeaconMember | 1,054.3 us-gaap_SupplementaryInsuranceInformationLiabilityForFuturePolicyBenefitsLossesClaimsAndLossExpenseReserves / us-gaap_StatementBusinessSegmentsAxis = wtm_OnebeaconMember | 1,000.0 us-gaap_SupplementaryInsuranceInformationLiabilityForFuturePolicyBenefitsLossesClaimsAndLossExpenseReserves / us-gaap_StatementBusinessSegmentsAxis = wtm_OnebeaconMember
Unearned premiums | 588.3 us-gaap_SupplementaryInsuranceInformationUnearnedPremiums / us-gaap_StatementBusinessSegmentsAxis = wtm_OnebeaconMember | 544.9 us-gaap_SupplementaryInsuranceInformationUnearnedPremiums / us-gaap_StatementBusinessSegmentsAxis = wtm_OnebeaconMember | 573.8 us-gaap_SupplementaryInsuranceInformationUnearnedPremiums / us-gaap_StatementBusinessSegmentsAxis = wtm_OnebeaconMember
Other policy claims and benefits payable | 0 us-gaap_SupplementaryInsuranceInformationOtherPolicyClaimsAndBenefitsPayable / us-gaap_StatementBusinessSegmentsAxis = wtm_OnebeaconMember | 0 us-gaap_SupplementaryInsuranceInformationOtherPolicyClaimsAndBenefitsPayable / us-gaap_StatementBusinessSegmentsAxis = wtm_OnebeaconMember | 0 us-gaap_SupplementaryInsuranceInformationOtherPolicyClaimsAndBenefitsPayable / us-gaap_StatementBusinessSegmentsAxis = wtm_OnebeaconMember
Premiums earned | 1,177.1 us-gaap_SupplementaryInsuranceInformationPremiumRevenue / us-gaap_StatementBusinessSegmentsAxis = wtm_OnebeaconMember | 1,120.4 us-gaap_SupplementaryInsuranceInformationPremiumRevenue / us-gaap_StatementBusinessSegmentsAxis = wtm_OnebeaconMember | 1,132.0 us-gaap_SupplementaryInsuranceInformationPremiumRevenue / us-gaap_StatementBusinessSegmentsAxis = wtm_OnebeaconMember
Net investment income | 41.7 us-gaap_SupplementaryInsuranceInformationNetInvestmentIncome / us-gaap_StatementBusinessSegmentsAxis = wtm_OnebeaconMember | 41.1 us-gaap_SupplementaryInsuranceInformationNetInvestmentIncome / us-gaap_StatementBusinessSegmentsAxis = wtm_OnebeaconMember | 53.6 us-gaap_SupplementaryInsuranceInformationNetInvestmentIncome / us-gaap_StatementBusinessSegmentsAxis = wtm_OnebeaconMember
Benefits, claims, losses, and settlement expenses | 815.1 us-gaap_SupplementaryInsuranceInformationBenefitsClaimsLossesAndSettlementExpense / us-gaap_StatementBusinessSegmentsAxis = wtm_OnebeaconMember | 622.1 us-gaap_SupplementaryInsuranceInformationBenefitsClaimsLossesAndSettlementExpense / us-gaap_StatementBusinessSegmentsAxis = wtm_OnebeaconMember | 650.0 us-gaap_SupplementaryInsuranceInformationBenefitsClaimsLossesAndSettlementExpense / us-gaap_StatementBusinessSegmentsAxis = wtm_OnebeaconMember
Amortization of deferred policy acquisition costs | 203.3 us-gaap_SupplementaryInsuranceInformationAmortizationOfDeferredPolicyAcquisitionCosts / us-gaap_StatementBusinessSegmentsAxis = wtm_OnebeaconMember | 208.9 us-gaap_SupplementaryInsuranceInformationAmortizationOfDeferredPolicyAcquisitionCosts / us-gaap_StatementBusinessSegmentsAxis = wtm_OnebeaconMember | 249.4 us-gaap_SupplementaryInsuranceInformationAmortizationOfDeferredPolicyAcquisitionCosts / us-gaap_StatementBusinessSegmentsAxis = wtm_OnebeaconMember
Other operating expenses | 179.2 us-gaap_SupplementaryInsuranceInformationOtherOperatingExpense / us-gaap_StatementBusinessSegmentsAxis = wtm_OnebeaconMember | 204.8 us-gaap_SupplementaryInsuranceInformationOtherOperatingExpense / us-gaap_StatementBusinessSegmentsAxis = wtm_OnebeaconMember | 205.2 us-gaap_SupplementaryInsuranceInformationOtherOperatingExpense / us-gaap_StatementBusinessSegmentsAxis = wtm_OnebeaconMember
Premiums written | 1,216.9 us-gaap_SupplementaryInsuranceInformationPremiumsWritten / us-gaap_StatementBusinessSegmentsAxis = wtm_OnebeaconMember | 1,088.6 us-gaap_SupplementaryInsuranceInformationPremiumsWritten / us-gaap_StatementBusinessSegmentsAxis = wtm_OnebeaconMember | 1,179.2 us-gaap_SupplementaryInsuranceInformationPremiumsWritten / us-gaap_StatementBusinessSegmentsAxis = wtm_OnebeaconMember
Net investment income | 41.7 us-gaap_NetInvestmentIncome / us-gaap_StatementBusinessSegmentsAxis = wtm_OnebeaconMember | 41.1 us-gaap_NetInvestmentIncome / us-gaap_StatementBusinessSegmentsAxis = wtm_OnebeaconMember | 53.6 us-gaap_NetInvestmentIncome / us-gaap_StatementBusinessSegmentsAxis = wtm_OnebeaconMember
Sirius Group |  |  |
SUPPLEMENTARY INSURANCE INFORMATION |  |  |
Deferred acquisition costs | 69.9 us-gaap_SupplementaryInsuranceInformationDeferredPolicyAcquisitionCosts / us-gaap_StatementBusinessSegmentsAxis = wtm_SiriusGroupSegmentMember | 69.3 us-gaap_SupplementaryInsuranceInformationDeferredPolicyAcquisitionCosts / us-gaap_StatementBusinessSegmentsAxis = wtm_SiriusGroupSegmentMember | 71.4 us-gaap_SupplementaryInsuranceInformationDeferredPolicyAcquisitionCosts / us-gaap_StatementBusinessSegmentsAxis = wtm_SiriusGroupSegmentMember
Future policy benefits, losses, claims and loss expenses | 1,809.8 us-gaap_SupplementaryInsuranceInformationLiabilityForFuturePolicyBenefitsLossesClaimsAndLossExpenseReserves / us-gaap_StatementBusinessSegmentsAxis = wtm_SiriusGroupSegmentMember | 2,025.0 us-gaap_SupplementaryInsuranceInformationLiabilityForFuturePolicyBenefitsLossesClaimsAndLossExpenseReserves / us-gaap_StatementBusinessSegmentsAxis = wtm_SiriusGroupSegmentMember | 2,168.9 us-gaap_SupplementaryInsuranceInformationLiabilityForFuturePolicyBenefitsLossesClaimsAndLossExpenseReserves / us-gaap_StatementBusinessSegmentsAxis = wtm_SiriusGroupSegmentMember
Unearned premiums | 338.6 us-gaap_SupplementaryInsuranceInformationUnearnedPremiums / us-gaap_StatementBusinessSegmentsAxis = wtm_SiriusGroupSegmentMember | 343.3 us-gaap_SupplementaryInsuranceInformationUnearnedPremiums / us-gaap_StatementBusinessSegmentsAxis = wtm_SiriusGroupSegmentMember | 350.2 us-gaap_SupplementaryInsuranceInformationUnearnedPremiums / us-gaap_StatementBusinessSegmentsAxis = wtm_SiriusGroupSegmentMember
Other policy claims and benefits payable | 0 us-gaap_SupplementaryInsuranceInformationOtherPolicyClaimsAndBenefitsPayable / us-gaap_StatementBusinessSegmentsAxis = wtm_SiriusGroupSegmentMember | 0 us-gaap_SupplementaryInsuranceInformationOtherPolicyClaimsAndBenefitsPayable / us-gaap_StatementBusinessSegmentsAxis = wtm_SiriusGroupSegmentMember | 0 us-gaap_SupplementaryInsuranceInformationOtherPolicyClaimsAndBenefitsPayable / us-gaap_StatementBusinessSegmentsAxis = wtm_SiriusGroupSegmentMember
Premiums earned | 873.9 us-gaap_SupplementaryInsuranceInformationPremiumRevenue / us-gaap_StatementBusinessSegmentsAxis = wtm_SiriusGroupSegmentMember | 866.4 us-gaap_SupplementaryInsuranceInformationPremiumRevenue / us-gaap_StatementBusinessSegmentsAxis = wtm_SiriusGroupSegmentMember | 931.6 us-gaap_SupplementaryInsuranceInformationPremiumRevenue / us-gaap_StatementBusinessSegmentsAxis = wtm_SiriusGroupSegmentMember
Net investment income | 41.1 us-gaap_SupplementaryInsuranceInformationNetInvestmentIncome / us-gaap_StatementBusinessSegmentsAxis = wtm_SiriusGroupSegmentMember | 30.3 us-gaap_SupplementaryInsuranceInformationNetInvestmentIncome / us-gaap_StatementBusinessSegmentsAxis = wtm_SiriusGroupSegmentMember | 65.0 us-gaap_SupplementaryInsuranceInformationNetInvestmentIncome / us-gaap_StatementBusinessSegmentsAxis = wtm_SiriusGroupSegmentMember
Benefits, claims, losses, and settlement expenses | 345.3 us-gaap_SupplementaryInsuranceInformationBenefitsClaimsLossesAndSettlementExpense / us-gaap_StatementBusinessSegmentsAxis = wtm_SiriusGroupSegmentMember | 418.4 us-gaap_SupplementaryInsuranceInformationBenefitsClaimsLossesAndSettlementExpense / us-gaap_StatementBusinessSegmentsAxis = wtm_SiriusGroupSegmentMember | 543.9 us-gaap_SupplementaryInsuranceInformationBenefitsClaimsLossesAndSettlementExpense / us-gaap_StatementBusinessSegmentsAxis = wtm_SiriusGroupSegmentMember
Amortization of deferred policy acquisition costs | 193.6 us-gaap_SupplementaryInsuranceInformationAmortizationOfDeferredPolicyAcquisitionCosts / us-gaap_StatementBusinessSegmentsAxis = wtm_SiriusGroupSegmentMember | 166.5 us-gaap_SupplementaryInsuranceInformationAmortizationOfDeferredPolicyAcquisitionCosts / us-gaap_StatementBusinessSegmentsAxis = wtm_SiriusGroupSegmentMember | 180.8 us-gaap_SupplementaryInsuranceInformationAmortizationOfDeferredPolicyAcquisitionCosts / us-gaap_StatementBusinessSegmentsAxis = wtm_SiriusGroupSegmentMember
Other operating expenses | 129.7 us-gaap_SupplementaryInsuranceInformationOtherOperatingExpense / us-gaap_StatementBusinessSegmentsAxis = wtm_SiriusGroupSegmentMember | 126.1 us-gaap_SupplementaryInsuranceInformationOtherOperatingExpense / us-gaap_StatementBusinessSegmentsAxis = wtm_SiriusGroupSegmentMember | 116.4 us-gaap_SupplementaryInsuranceInformationOtherOperatingExpense / us-gaap_StatementBusinessSegmentsAxis = wtm_SiriusGroupSegmentMember
Premiums written | 882.5 us-gaap_SupplementaryInsuranceInformationPremiumsWritten / us-gaap_StatementBusinessSegmentsAxis = wtm_SiriusGroupSegmentMember | 876.6 us-gaap_SupplementaryInsuranceInformationPremiumsWritten / us-gaap_StatementBusinessSegmentsAxis = wtm_SiriusGroupSegmentMember | 947.7 us-gaap_SupplementaryInsuranceInformationPremiumsWritten / us-gaap_StatementBusinessSegmentsAxis = wtm_SiriusGroupSegmentMember
HG Global-BAM |  |  |
SUPPLEMENTARY INSURANCE INFORMATION |  |  |
Deferred acquisition costs | 4.0 us-gaap_SupplementaryInsuranceInformationDeferredPolicyAcquisitionCosts / us-gaap_StatementBusinessSegmentsAxis = wtm_HgGlobalBamMember | 1.7 us-gaap_SupplementaryInsuranceInformationDeferredPolicyAcquisitionCosts / us-gaap_StatementBusinessSegmentsAxis = wtm_HgGlobalBamMember |
Future policy benefits, losses, claims and loss expenses | 0 us-gaap_SupplementaryInsuranceInformationLiabilityForFuturePolicyBenefitsLossesClaimsAndLossExpenseReserves / us-gaap_StatementBusinessSegmentsAxis = wtm_HgGlobalBamMember | 0 us-gaap_SupplementaryInsuranceInformationLiabilityForFuturePolicyBenefitsLossesClaimsAndLossExpenseReserves / us-gaap_StatementBusinessSegmentsAxis = wtm_HgGlobalBamMember |
Unearned premiums | 27.6 us-gaap_SupplementaryInsuranceInformationUnearnedPremiums / us-gaap_StatementBusinessSegmentsAxis = wtm_HgGlobalBamMember | 13.2 us-gaap_SupplementaryInsuranceInformationUnearnedPremiums / us-gaap_StatementBusinessSegmentsAxis = wtm_HgGlobalBamMember |
Other policy claims and benefits payable | 0 us-gaap_SupplementaryInsuranceInformationOtherPolicyClaimsAndBenefitsPayable / us-gaap_StatementBusinessSegmentsAxis = wtm_HgGlobalBamMember | 0 us-gaap_SupplementaryInsuranceInformationOtherPolicyClaimsAndBenefitsPayable / us-gaap_StatementBusinessSegmentsAxis = wtm_HgGlobalBamMember |
Premiums earned | 1.8 us-gaap_SupplementaryInsuranceInformationPremiumRevenue / us-gaap_StatementBusinessSegmentsAxis = wtm_HgGlobalBamMember | 0.5 us-gaap_SupplementaryInsuranceInformationPremiumRevenue / us-gaap_StatementBusinessSegmentsAxis = wtm_HgGlobalBamMember |
Net investment income | 7.1 us-gaap_SupplementaryInsuranceInformationNetInvestmentIncome / us-gaap_StatementBusinessSegmentsAxis = wtm_HgGlobalBamMember | 5.7 us-gaap_SupplementaryInsuranceInformationNetInvestmentIncome / us-gaap_StatementBusinessSegmentsAxis = wtm_HgGlobalBamMember |
Benefits, claims, losses, and settlement expenses | 0 us-gaap_SupplementaryInsuranceInformationBenefitsClaimsLossesAndSettlementExpense / us-gaap_StatementBusinessSegmentsAxis = wtm_HgGlobalBamMember | 0 us-gaap_SupplementaryInsuranceInformationBenefitsClaimsLossesAndSettlementExpense / us-gaap_StatementBusinessSegmentsAxis = wtm_HgGlobalBamMember |
Amortization of deferred policy acquisition costs | 2.1 us-gaap_SupplementaryInsuranceInformationAmortizationOfDeferredPolicyAcquisitionCosts / us-gaap_StatementBusinessSegmentsAxis = wtm_HgGlobalBamMember | 1.5 us-gaap_SupplementaryInsuranceInformationAmortizationOfDeferredPolicyAcquisitionCosts / us-gaap_StatementBusinessSegmentsAxis = wtm_HgGlobalBamMember |
Other operating expenses | 0.4 us-gaap_SupplementaryInsuranceInformationOtherOperatingExpense / us-gaap_StatementBusinessSegmentsAxis = wtm_HgGlobalBamMember | 0.4 us-gaap_SupplementaryInsuranceInformationOtherOperatingExpense / us-gaap_StatementBusinessSegmentsAxis = wtm_HgGlobalBamMember |
Premiums written | 16.2 us-gaap_SupplementaryInsuranceInformationPremiumsWritten / us-gaap_StatementBusinessSegmentsAxis = wtm_HgGlobalBamMember | 13.6 us-gaap_SupplementaryInsuranceInformationPremiumsWritten / us-gaap_StatementBusinessSegmentsAxis = wtm_HgGlobalBamMember |
Other Operations |  |  |
SUPPLEMENTARY INSURANCE INFORMATION |  |  |
Deferred acquisition costs | 0 us-gaap_SupplementaryInsuranceInformationDeferredPolicyAcquisitionCosts / us-gaap_StatementBusinessSegmentsAxis = wtm_OtherOperationsMember | 0 us-gaap_SupplementaryInsuranceInformationDeferredPolicyAcquisitionCosts / us-gaap_StatementBusinessSegmentsAxis = wtm_OtherOperationsMember | 0 us-gaap_SupplementaryInsuranceInformationDeferredPolicyAcquisitionCosts / us-gaap_StatementBusinessSegmentsAxis = wtm_OtherOperationsMember
Future policy benefits, losses, claims and loss expenses | 7.8 us-gaap_SupplementaryInsuranceInformationLiabilityForFuturePolicyBenefitsLossesClaimsAndLossExpenseReserves / us-gaap_StatementBusinessSegmentsAxis = wtm_OtherOperationsMember | 0 us-gaap_SupplementaryInsuranceInformationLiabilityForFuturePolicyBenefitsLossesClaimsAndLossExpenseReserves / us-gaap_StatementBusinessSegmentsAxis = wtm_OtherOperationsMember | 0 us-gaap_SupplementaryInsuranceInformationLiabilityForFuturePolicyBenefitsLossesClaimsAndLossExpenseReserves / us-gaap_StatementBusinessSegmentsAxis = wtm_OtherOperationsMember
Unearned premiums | 0.8 us-gaap_SupplementaryInsuranceInformationUnearnedPremiums / us-gaap_StatementBusinessSegmentsAxis = wtm_OtherOperationsMember | 0 us-gaap_SupplementaryInsuranceInformationUnearnedPremiums / us-gaap_StatementBusinessSegmentsAxis = wtm_OtherOperationsMember | 0 us-gaap_SupplementaryInsuranceInformationUnearnedPremiums / us-gaap_StatementBusinessSegmentsAxis = wtm_OtherOperationsMember
Other policy claims and benefits payable | 0 us-gaap_SupplementaryInsuranceInformationOtherPolicyClaimsAndBenefitsPayable / us-gaap_StatementBusinessSegmentsAxis = wtm_OtherOperationsMember | 0 us-gaap_SupplementaryInsuranceInformationOtherPolicyClaimsAndBenefitsPayable / us-gaap_StatementBusinessSegmentsAxis = wtm_OtherOperationsMember | 0 us-gaap_SupplementaryInsuranceInformationOtherPolicyClaimsAndBenefitsPayable / us-gaap_StatementBusinessSegmentsAxis = wtm_OtherOperationsMember
Premiums earned | 6.1 us-gaap_SupplementaryInsuranceInformationPremiumRevenue / us-gaap_StatementBusinessSegmentsAxis = wtm_OtherOperationsMember | 0 us-gaap_SupplementaryInsuranceInformationPremiumRevenue / us-gaap_StatementBusinessSegmentsAxis = wtm_OtherOperationsMember | 0 us-gaap_SupplementaryInsuranceInformationPremiumRevenue / us-gaap_StatementBusinessSegmentsAxis = wtm_OtherOperationsMember
Net investment income | 0.2 us-gaap_SupplementaryInsuranceInformationNetInvestmentIncome / us-gaap_StatementBusinessSegmentsAxis = wtm_OtherOperationsMember | 0.1 us-gaap_SupplementaryInsuranceInformationNetInvestmentIncome / us-gaap_StatementBusinessSegmentsAxis = wtm_OtherOperationsMember | 0.5 us-gaap_SupplementaryInsuranceInformationNetInvestmentIncome / us-gaap_StatementBusinessSegmentsAxis = wtm_OtherOperationsMember
Benefits, claims, losses, and settlement expenses | 8.9 us-gaap_SupplementaryInsuranceInformationBenefitsClaimsLossesAndSettlementExpense / us-gaap_StatementBusinessSegmentsAxis = wtm_OtherOperationsMember | 0 us-gaap_SupplementaryInsuranceInformationBenefitsClaimsLossesAndSettlementExpense / us-gaap_StatementBusinessSegmentsAxis = wtm_OtherOperationsMember | 0 us-gaap_SupplementaryInsuranceInformationBenefitsClaimsLossesAndSettlementExpense / us-gaap_StatementBusinessSegmentsAxis = wtm_OtherOperationsMember
Amortization of deferred policy acquisition costs | 0.8 us-gaap_SupplementaryInsuranceInformationAmortizationOfDeferredPolicyAcquisitionCosts / us-gaap_StatementBusinessSegmentsAxis = wtm_OtherOperationsMember | 0 us-gaap_SupplementaryInsuranceInformationAmortizationOfDeferredPolicyAcquisitionCosts / us-gaap_StatementBusinessSegmentsAxis = wtm_OtherOperationsMember | 0 us-gaap_SupplementaryInsuranceInformationAmortizationOfDeferredPolicyAcquisitionCosts / us-gaap_StatementBusinessSegmentsAxis = wtm_OtherOperationsMember
Other operating expenses | 0 us-gaap_SupplementaryInsuranceInformationOtherOperatingExpense / us-gaap_StatementBusinessSegmentsAxis = wtm_OtherOperationsMember | 0 us-gaap_SupplementaryInsuranceInformationOtherOperatingExpense / us-gaap_StatementBusinessSegmentsAxis = wtm_OtherOperationsMember | 0 us-gaap_SupplementaryInsuranceInformationOtherOperatingExpense / us-gaap_StatementBusinessSegmentsAxis = wtm_OtherOperationsMember
Premiums written | 5.9 us-gaap_SupplementaryInsuranceInformationPremiumsWritten / us-gaap_StatementBusinessSegmentsAxis = wtm_OtherOperationsMember | 0 us-gaap_SupplementaryInsuranceInformationPremiumsWritten / us-gaap_StatementBusinessSegmentsAxis = wtm_OtherOperationsMember | 0 us-gaap_SupplementaryInsuranceInformationPremiumsWritten / us-gaap_StatementBusinessSegmentsAxis = wtm_OtherOperationsMember
Non-insurance [Member] | Operating Segments |  |  |
SUPPLEMENTARY INSURANCE INFORMATION |  |  |
Net investment income | $ 14.9 us-gaap_NetInvestmentIncome / us-gaap_StatementBusinessSegmentsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementOperatingActivitiesSegmentAxis = wtm_NoninsuranceMember | $ 33.7 us-gaap_NetInvestmentIncome / us-gaap_StatementBusinessSegmentsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementOperatingActivitiesSegmentAxis = wtm_NoninsuranceMember | $ 32.3 us-gaap_NetInvestmentIncome / us-gaap_StatementBusinessSegmentsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementOperatingActivitiesSegmentAxis = wtm_NoninsuranceMember

X
- Definition Amount, after investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 16 -Article 12 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04.2) -URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph 2 -Article 7 + Details
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- Definition Amount of amortization of deferred policy acquisition costs recognized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 16 -Article 12 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 235 -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-16) -URI http://asc.fasb.org/extlink&oid=6588446&loc=d3e574960-122915 + Details
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- Definition Amount of insurance benefits, claims, losses and settlement expenses incurred. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 16 -Article 12 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 235 -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-16) -URI http://asc.fasb.org/extlink&oid=6588446&loc=d3e574960-122915 + Details
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- Definition Net amount of deferred policy acquisition costs capitalized on contracts remaining in force on the balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 16 -Article 12 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 235 -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-16) -URI http://asc.fasb.org/extlink&oid=6588446&loc=d3e574960-122915 + Details
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- Definition Amount of reserves for future policy claims payable and loss expenses to be incurred. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 16 -Article 12 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 235 -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-16) -URI http://asc.fasb.org/extlink&oid=6588446&loc=d3e574960-122915 + Details
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- Definition Amount of net investment income earned. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 16 -Article 12 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 235 -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-16) -URI http://asc.fasb.org/extlink&oid=6588446&loc=d3e574960-122915 + Details
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- Definition Amount of other operating expense incurred. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 16 -Article 12 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 235 -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-16) -URI http://asc.fasb.org/extlink&oid=6588446&loc=d3e574960-122915 + Details
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- Definition Amount of claims and benefits payable not included within other categories. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 16 -Article 12 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 235 -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-16) -URI http://asc.fasb.org/extlink&oid=6588446&loc=d3e574960-122915 + Details
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- Definition Amount of premium revenue earned. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 16 -Article 12 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 235 -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-16) -URI http://asc.fasb.org/extlink&oid=6588446&loc=d3e574960-122915 + Details
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- Definition Amount of premiums not yet earned. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 16 -Article 12 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 235 -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-16) -URI http://asc.fasb.org/extlink&oid=6588446&loc=d3e574960-122915 + Details
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- Details
Name: | us-gaap_StatementOperatingActivitiesSegmentAxis=wtm_NoninsuranceMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |