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Investment Securities (Restrictions on Redemption Frequency and Advance Notice Requirements) (Details) (Hedge funds, USD $) In Millions, unless otherwise specified | Dec. 31, 2014
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Investment securities |
Trading Securities, Other | $ 92.0 us-gaap_TradingSecuritiesOther
Distributions from inactive hedge funds | 2.1 wtm_DistributionsFromInactiveHedgeFunds
Outstanding redemptions | 6.7 wtm_Outstandingredemptions
30-59 days notice |
Investment securities |
Trading Securities, Other | 36.1 us-gaap_TradingSecuritiesOther / wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyAxis = wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionNoticePeriod30To59DaysMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_HedgeFundsMember
60-89 days notice |
Investment securities |
Trading Securities, Other | 43.5 us-gaap_TradingSecuritiesOther / wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyAxis = wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionNoticePeriod60To89DaysMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_HedgeFundsMember
90-119 days notice |
Investment securities |
Trading Securities, Other | 4.4 us-gaap_TradingSecuritiesOther / wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyAxis = wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionNoticePeriod90To119DaysMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_HedgeFundsMember
120 days notice |
Investment securities |
Trading Securities, Other | 8.0 us-gaap_TradingSecuritiesOther / wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyAxis = wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionNoticePeriodOver120DaysMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_HedgeFundsMember
Monthly |
Investment securities |
Trading Securities, Other | 4.3 us-gaap_TradingSecuritiesOther / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_HedgeFundsMember / wtm_RedemptionFrequencyAxis = wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyMonthlyMember
Monthly | 30-59 days notice |
Investment securities |
Trading Securities, Other | 4.3 us-gaap_TradingSecuritiesOther / wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyAxis = wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionNoticePeriod30To59DaysMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_HedgeFundsMember / wtm_RedemptionFrequencyAxis = wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyMonthlyMember
Monthly | 60-89 days notice |
Investment securities |
Trading Securities, Other | 0 us-gaap_TradingSecuritiesOther / wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyAxis = wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionNoticePeriod60To89DaysMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_HedgeFundsMember / wtm_RedemptionFrequencyAxis = wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyMonthlyMember
Monthly | 90-119 days notice |
Investment securities |
Trading Securities, Other | 0 us-gaap_TradingSecuritiesOther / wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyAxis = wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionNoticePeriod90To119DaysMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_HedgeFundsMember / wtm_RedemptionFrequencyAxis = wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyMonthlyMember
Monthly | 120 days notice |
Investment securities |
Trading Securities, Other | 0 us-gaap_TradingSecuritiesOther / wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyAxis = wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionNoticePeriodOver120DaysMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_HedgeFundsMember / wtm_RedemptionFrequencyAxis = wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyMonthlyMember
Quarterly |
Investment securities |
Trading Securities, Other | 61.0 us-gaap_TradingSecuritiesOther / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_HedgeFundsMember / wtm_RedemptionFrequencyAxis = wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyQuarterlyMember
Quarterly | 30-59 days notice |
Investment securities |
Trading Securities, Other | 31.8 us-gaap_TradingSecuritiesOther / wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyAxis = wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionNoticePeriod30To59DaysMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_HedgeFundsMember / wtm_RedemptionFrequencyAxis = wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyQuarterlyMember
Quarterly | 60-89 days notice |
Investment securities |
Trading Securities, Other | 21.4 us-gaap_TradingSecuritiesOther / wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyAxis = wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionNoticePeriod60To89DaysMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_HedgeFundsMember / wtm_RedemptionFrequencyAxis = wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyQuarterlyMember
Quarterly | 90-119 days notice |
Investment securities |
Trading Securities, Other | 0 us-gaap_TradingSecuritiesOther / wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyAxis = wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionNoticePeriod90To119DaysMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_HedgeFundsMember / wtm_RedemptionFrequencyAxis = wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyQuarterlyMember
Quarterly | 120 days notice |
Investment securities |
Trading Securities, Other | 7.8 us-gaap_TradingSecuritiesOther / wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyAxis = wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionNoticePeriodOver120DaysMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_HedgeFundsMember / wtm_RedemptionFrequencyAxis = wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyQuarterlyMember
Semi-annual |
Investment securities |
Trading Securities, Other | 22.1 us-gaap_TradingSecuritiesOther / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_HedgeFundsMember / wtm_RedemptionFrequencyAxis = wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencySemiAnnualMember
Semi-annual | 30-59 days notice |
Investment securities |
Trading Securities, Other | 0 us-gaap_TradingSecuritiesOther / wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyAxis = wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionNoticePeriod30To59DaysMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_HedgeFundsMember / wtm_RedemptionFrequencyAxis = wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencySemiAnnualMember
Semi-annual | 60-89 days notice |
Investment securities |
Trading Securities, Other | 22.1 us-gaap_TradingSecuritiesOther / wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyAxis = wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionNoticePeriod60To89DaysMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_HedgeFundsMember / wtm_RedemptionFrequencyAxis = wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencySemiAnnualMember
Semi-annual | 90-119 days notice |
Investment securities |
Trading Securities, Other | 0 us-gaap_TradingSecuritiesOther / wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyAxis = wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionNoticePeriod90To119DaysMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_HedgeFundsMember / wtm_RedemptionFrequencyAxis = wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencySemiAnnualMember
Semi-annual | 120 days notice |
Investment securities |
Trading Securities, Other | 0 us-gaap_TradingSecuritiesOther / wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyAxis = wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionNoticePeriodOver120DaysMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_HedgeFundsMember / wtm_RedemptionFrequencyAxis = wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencySemiAnnualMember
Annual |
Investment securities |
Trading Securities, Other | 4.6 us-gaap_TradingSecuritiesOther / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_HedgeFundsMember / wtm_RedemptionFrequencyAxis = wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyAnnualMember
Annual | 30-59 days notice |
Investment securities |
Trading Securities, Other | 0 us-gaap_TradingSecuritiesOther / wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyAxis = wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionNoticePeriod30To59DaysMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_HedgeFundsMember / wtm_RedemptionFrequencyAxis = wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyAnnualMember
Annual | 60-89 days notice |
Investment securities |
Trading Securities, Other | 0 us-gaap_TradingSecuritiesOther / wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyAxis = wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionNoticePeriod60To89DaysMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_HedgeFundsMember / wtm_RedemptionFrequencyAxis = wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyAnnualMember
Annual | 90-119 days notice |
Investment securities |
Trading Securities, Other | 4.4 us-gaap_TradingSecuritiesOther / wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyAxis = wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionNoticePeriod90To119DaysMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_HedgeFundsMember / wtm_RedemptionFrequencyAxis = wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyAnnualMember
Annual | 120 days notice |
Investment securities |
Trading Securities, Other | $ 0.2 us-gaap_TradingSecuritiesOther / wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyAxis = wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionNoticePeriodOver120DaysMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_HedgeFundsMember / wtm_RedemptionFrequencyAxis = wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyAnnualMember

X
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- Definition Amount of other investments classified as trading. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26626-111562 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.4) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Trading Securities -URI http://asc.fasb.org/extlink&oid=6526789 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.(a),1(c),(d),(e),(f),(g)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 1 -Subparagraph c, d, e, f, g -Article 7 + Details
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- Definition Distributions pending from hedge funds that are no longer active and are in process of disposing their underlying investments. + References No definition available. + Details
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- Definition Outstanding redemptions that are subject to market fluctuations. + References No definition available. + Details
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