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v2.4.1.9

Employee Share-Based Incentive Compensation Plans (OneBeacon - Restricted Stock Units) (Details) (Restricted Stock Units (RSUs) [Member], OneBeacon, One Beacon Long Term Incentive Plan, USD $) In Millions, except Share data, unless otherwise specified | 0 Months Ended | 3 Months Ended
--- | --- | ---
Feb. 24, 2015 | Mar. 31, 2015
Restricted Stock Units (RSUs) [Member] | OneBeacon | One Beacon Long Term Incentive Plan |  |
Share-based compensation arrangement by share-based payment award |  |
Issued (in shares) | 207,848 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockUnitsRSUMember / dei_LegalEntityAxis = wtm_OnebeaconMember / us-gaap_PlanNameAxis = wtm_LongTermIncentivePlanMember |
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding, Number |  | 205,319 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockUnitsRSUMember / dei_LegalEntityAxis = wtm_OnebeaconMember / us-gaap_PlanNameAxis = wtm_LongTermIncentivePlanMember
Expense recognized |  | $ 0.1 us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockUnitsRSUMember / dei_LegalEntityAxis = wtm_OnebeaconMember / us-gaap_PlanNameAxis = wtm_LongTermIncentivePlanMember

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- Definition Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 14.F) -URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1)(i) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 14 -Section F + Details
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- Details
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- Definition Number of equity instruments other than options outstanding, including both vested and non-vested instruments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(i) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(ii) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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Period Type: | instant

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- Definition Number of share instruments newly issued under a share-based compensation plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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