XML 100 R96.htm IDEA: XBRL DOCUMENT
v2.4.1.9

Goodwill and Other Intangible Assets (Goodwill and Intangible Assets) (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended |  |  |  |  |
--- | --- | --- | --- | --- | --- | ---
Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012 | Oct. 10, 2014 | Mar. 14, 2014 | Feb. 19, 2014
Goodwill [Line Items] |  |  |  |  |  |
Intangible Assets, Gross (Excluding Goodwill) | $ 213.5 us-gaap_IntangibleAssetsGrossExcludingGoodwill | $ 25.0 us-gaap_IntangibleAssetsGrossExcludingGoodwill |  |  |  |
Amortization of Intangible Assets | 16.0 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization | 4.3 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization |  |  |  |
Intangible Assets, Net (Excluding Goodwill) | 197.5 us-gaap_IntangibleAssetsNetExcludingGoodwill | 20.7 us-gaap_IntangibleAssetsNetExcludingGoodwill | 16.9 us-gaap_IntangibleAssetsNetExcludingGoodwill |  |  |
Goodwill | 168.9 us-gaap_Goodwill | 0 us-gaap_Goodwill | 0 us-gaap_Goodwill |  |  |
Intangible Assets, Gross (Including Goodwill) | 382.4 wtm_IntangibleAssetsGrossIncludingGoodwill | 25.0 wtm_IntangibleAssetsGrossIncludingGoodwill |  |  |  |
Goodwill and intangible assets | 366.4 us-gaap_IntangibleAssetsNetIncludingGoodwill | 20.7 us-gaap_IntangibleAssetsNetIncludingGoodwill |  |  |  |
Tranzact [Member] |  |  |  |  |  |
Goodwill [Line Items] |  |  |  |  |  |
Intangible Assets, Gross (Excluding Goodwill) | 146.3 us-gaap_IntangibleAssetsGrossExcludingGoodwill / dei_LegalEntityAxis = wtm_TranzactMember | 0 us-gaap_IntangibleAssetsGrossExcludingGoodwill / dei_LegalEntityAxis = wtm_TranzactMember |  |  |  |
Amortization of Intangible Assets | 3.5 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / dei_LegalEntityAxis = wtm_TranzactMember | 0 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / dei_LegalEntityAxis = wtm_TranzactMember |  |  |  |
Intangible Assets, Net (Excluding Goodwill) | 142.8 us-gaap_IntangibleAssetsNetExcludingGoodwill / dei_LegalEntityAxis = wtm_TranzactMember | 0 us-gaap_IntangibleAssetsNetExcludingGoodwill / dei_LegalEntityAxis = wtm_TranzactMember |  | 146.3 us-gaap_IntangibleAssetsNetExcludingGoodwill / dei_LegalEntityAxis = wtm_TranzactMember |  |
Goodwill | 145.1 us-gaap_Goodwill / dei_LegalEntityAxis = wtm_TranzactMember | 0 us-gaap_Goodwill / dei_LegalEntityAxis = wtm_TranzactMember |  | 145.1 us-gaap_Goodwill / dei_LegalEntityAxis = wtm_TranzactMember |  |
QuoteLab [Member] |  |  |  |  |  |
Goodwill [Line Items] |  |  |  |  |  |
Intangible Assets, Gross (Excluding Goodwill) | 38.5 us-gaap_IntangibleAssetsGrossExcludingGoodwill / dei_LegalEntityAxis = wtm_QuoteLabMember | 0 us-gaap_IntangibleAssetsGrossExcludingGoodwill / dei_LegalEntityAxis = wtm_QuoteLabMember |  |  |  |
Amortization of Intangible Assets | 6.0 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / dei_LegalEntityAxis = wtm_QuoteLabMember | 0 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / dei_LegalEntityAxis = wtm_QuoteLabMember |  |  |  |
Intangible Assets, Net (Excluding Goodwill) | 32.5 us-gaap_IntangibleAssetsNetExcludingGoodwill / dei_LegalEntityAxis = wtm_QuoteLabMember | 0 us-gaap_IntangibleAssetsNetExcludingGoodwill / dei_LegalEntityAxis = wtm_QuoteLabMember |  |  | 38.5 us-gaap_IntangibleAssetsNetExcludingGoodwill / dei_LegalEntityAxis = wtm_QuoteLabMember |
Goodwill | 18.3 us-gaap_Goodwill / dei_LegalEntityAxis = wtm_QuoteLabMember | 0 us-gaap_Goodwill / dei_LegalEntityAxis = wtm_QuoteLabMember |  |  | 18.3 us-gaap_Goodwill / dei_LegalEntityAxis = wtm_QuoteLabMember |
WOBI [Member] |  |  |  |  |  |
Goodwill [Line Items] |  |  |  |  |  |
Intangible Assets, Gross (Excluding Goodwill) | 2.9 us-gaap_IntangibleAssetsGrossExcludingGoodwill / dei_LegalEntityAxis = wtm_WOBIMember | 0 us-gaap_IntangibleAssetsGrossExcludingGoodwill / dei_LegalEntityAxis = wtm_WOBIMember |  |  |  |
Amortization of Intangible Assets | 0.4 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / dei_LegalEntityAxis = wtm_WOBIMember | 0 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / dei_LegalEntityAxis = wtm_WOBIMember |  |  |  |
Intangible Assets, Net (Excluding Goodwill) | 2.5 us-gaap_IntangibleAssetsNetExcludingGoodwill / dei_LegalEntityAxis = wtm_WOBIMember | 0 us-gaap_IntangibleAssetsNetExcludingGoodwill / dei_LegalEntityAxis = wtm_WOBIMember |  |  |  |
Goodwill | 5.5 us-gaap_Goodwill / dei_LegalEntityAxis = wtm_WOBIMember | 0 us-gaap_Goodwill / dei_LegalEntityAxis = wtm_WOBIMember |  |  |  | 5.5 us-gaap_Goodwill / dei_LegalEntityAxis = wtm_WOBIMember
Developed Technology Rights [Member] | Tranzact [Member] |  |  |  |  |  |
Goodwill [Line Items] |  |  |  |  |  |
Intangible Assets, Gross (Excluding Goodwill) | 12.7 us-gaap_IntangibleAssetsGrossExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_DevelopedTechnologyRightsMember / dei_LegalEntityAxis = wtm_TranzactMember | 0 us-gaap_IntangibleAssetsGrossExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_DevelopedTechnologyRightsMember / dei_LegalEntityAxis = wtm_TranzactMember |  |  |  |
Amortization of Intangible Assets | 0.5 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_DevelopedTechnologyRightsMember / dei_LegalEntityAxis = wtm_TranzactMember | 0 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_DevelopedTechnologyRightsMember / dei_LegalEntityAxis = wtm_TranzactMember |  |  |  |
Intangible Assets, Net (Excluding Goodwill) | 12.2 us-gaap_IntangibleAssetsNetExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_DevelopedTechnologyRightsMember / dei_LegalEntityAxis = wtm_TranzactMember | 0 us-gaap_IntangibleAssetsNetExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_DevelopedTechnologyRightsMember / dei_LegalEntityAxis = wtm_TranzactMember |  |  |  |
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life | 5 years |  |  |  |  |
Developed Technology Rights [Member] | QuoteLab [Member] |  |  |  |  |  |
Goodwill [Line Items] |  |  |  |  |  |
Intangible Assets, Gross (Excluding Goodwill) | 32.0 us-gaap_IntangibleAssetsGrossExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_DevelopedTechnologyRightsMember / dei_LegalEntityAxis = wtm_QuoteLabMember | 0 us-gaap_IntangibleAssetsGrossExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_DevelopedTechnologyRightsMember / dei_LegalEntityAxis = wtm_QuoteLabMember |  |  |  |
Amortization of Intangible Assets | 4.8 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_DevelopedTechnologyRightsMember / dei_LegalEntityAxis = wtm_QuoteLabMember | 0 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_DevelopedTechnologyRightsMember / dei_LegalEntityAxis = wtm_QuoteLabMember |  |  |  |
Intangible Assets, Net (Excluding Goodwill) | 27.2 us-gaap_IntangibleAssetsNetExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_DevelopedTechnologyRightsMember / dei_LegalEntityAxis = wtm_QuoteLabMember | 0 us-gaap_IntangibleAssetsNetExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_DevelopedTechnologyRightsMember / dei_LegalEntityAxis = wtm_QuoteLabMember |  |  |  |
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life | 5 years |  |  |  |  |
Developed Technology Rights [Member] | WOBI [Member] |  |  |  |  |  |
Goodwill [Line Items] |  |  |  |  |  |
Intangible Assets, Gross (Excluding Goodwill) | 0.8 us-gaap_IntangibleAssetsGrossExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_DevelopedTechnologyRightsMember / dei_LegalEntityAxis = wtm_WOBIMember | 0 us-gaap_IntangibleAssetsGrossExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_DevelopedTechnologyRightsMember / dei_LegalEntityAxis = wtm_WOBIMember |  |  |  |
Amortization of Intangible Assets | 0.2 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_DevelopedTechnologyRightsMember / dei_LegalEntityAxis = wtm_WOBIMember | 0 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_DevelopedTechnologyRightsMember / dei_LegalEntityAxis = wtm_WOBIMember |  |  |  |
Intangible Assets, Net (Excluding Goodwill) | 0.6 us-gaap_IntangibleAssetsNetExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_DevelopedTechnologyRightsMember / dei_LegalEntityAxis = wtm_WOBIMember | 0 us-gaap_IntangibleAssetsNetExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_DevelopedTechnologyRightsMember / dei_LegalEntityAxis = wtm_WOBIMember |  |  |  |
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life | 3 years |  |  |  |  |
Customer Relationships [Member] |  |  |  |  |  |
Goodwill [Line Items] |  |  |  |  |  |
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life | 3 years |  |  |  |  |
Customer Relationships [Member] | Tranzact [Member] |  |  |  |  |  |
Goodwill [Line Items] |  |  |  |  |  |
Intangible Assets, Gross (Excluding Goodwill) | 107.5 us-gaap_IntangibleAssetsGrossExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_CustomerRelationshipsMember / dei_LegalEntityAxis = wtm_TranzactMember | 0 us-gaap_IntangibleAssetsGrossExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_CustomerRelationshipsMember / dei_LegalEntityAxis = wtm_TranzactMember |  |  |  |
Amortization of Intangible Assets | 2.1 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_CustomerRelationshipsMember / dei_LegalEntityAxis = wtm_TranzactMember | 0 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_CustomerRelationshipsMember / dei_LegalEntityAxis = wtm_TranzactMember |  |  |  |
Intangible Assets, Net (Excluding Goodwill) | 105.4 us-gaap_IntangibleAssetsNetExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_CustomerRelationshipsMember / dei_LegalEntityAxis = wtm_TranzactMember | 0 us-gaap_IntangibleAssetsNetExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_CustomerRelationshipsMember / dei_LegalEntityAxis = wtm_TranzactMember |  |  |  |
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life | 10 years |  |  |  |  |
Customer Relationships [Member] | QuoteLab [Member] |  |  |  |  |  |
Goodwill [Line Items] |  |  |  |  |  |
Intangible Assets, Gross (Excluding Goodwill) | 6.5 us-gaap_IntangibleAssetsGrossExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_CustomerRelationshipsMember / dei_LegalEntityAxis = wtm_QuoteLabMember | 0 us-gaap_IntangibleAssetsGrossExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_CustomerRelationshipsMember / dei_LegalEntityAxis = wtm_QuoteLabMember |  |  |  |
Amortization of Intangible Assets | 1.2 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_CustomerRelationshipsMember / dei_LegalEntityAxis = wtm_QuoteLabMember | 0 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_CustomerRelationshipsMember / dei_LegalEntityAxis = wtm_QuoteLabMember |  |  |  |
Intangible Assets, Net (Excluding Goodwill) | 5.3 us-gaap_IntangibleAssetsNetExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_CustomerRelationshipsMember / dei_LegalEntityAxis = wtm_QuoteLabMember | 0 us-gaap_IntangibleAssetsNetExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_CustomerRelationshipsMember / dei_LegalEntityAxis = wtm_QuoteLabMember |  |  |  |
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life | 4 years |  |  |  |  |
Customer Relationships [Member] | Star & Shield Insurance Exchange [Member] |  |  |  |  |  |
Goodwill [Line Items] |  |  |  |  |  |
Intangible Assets, Gross (Excluding Goodwill) | 1.2 us-gaap_IntangibleAssetsGrossExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_CustomerRelationshipsMember / dei_LegalEntityAxis = wtm_StarShieldInsuranceExchangeMember | 0 us-gaap_IntangibleAssetsGrossExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_CustomerRelationshipsMember / dei_LegalEntityAxis = wtm_StarShieldInsuranceExchangeMember |  |  |  |
Amortization of Intangible Assets | 0.4 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_CustomerRelationshipsMember / dei_LegalEntityAxis = wtm_StarShieldInsuranceExchangeMember | 0 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_CustomerRelationshipsMember / dei_LegalEntityAxis = wtm_StarShieldInsuranceExchangeMember |  |  |  |
Intangible Assets, Net (Excluding Goodwill) | 0.8 us-gaap_IntangibleAssetsNetExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_CustomerRelationshipsMember / dei_LegalEntityAxis = wtm_StarShieldInsuranceExchangeMember | 0 us-gaap_IntangibleAssetsNetExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_CustomerRelationshipsMember / dei_LegalEntityAxis = wtm_StarShieldInsuranceExchangeMember |  |  |  |
Trademarks [Member] | WOBI [Member] |  |  |  |  |  |
Goodwill [Line Items] |  |  |  |  |  |
Intangible Assets, Gross (Excluding Goodwill) | 2.1 us-gaap_IntangibleAssetsGrossExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_TrademarksMember / dei_LegalEntityAxis = wtm_WOBIMember | 0 us-gaap_IntangibleAssetsGrossExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_TrademarksMember / dei_LegalEntityAxis = wtm_WOBIMember |  |  |  |
Amortization of Intangible Assets | 0.2 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_TrademarksMember / dei_LegalEntityAxis = wtm_WOBIMember | 0 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_TrademarksMember / dei_LegalEntityAxis = wtm_WOBIMember |  |  |  |
Intangible Assets, Net (Excluding Goodwill) | 1.9 us-gaap_IntangibleAssetsNetExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_TrademarksMember / dei_LegalEntityAxis = wtm_WOBIMember | 0 us-gaap_IntangibleAssetsNetExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_TrademarksMember / dei_LegalEntityAxis = wtm_WOBIMember |  |  |  |
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life | 8 years |  |  |  |  |
Other Intangible Assets [Member] | Tranzact [Member] |  |  |  |  |  |
Goodwill [Line Items] |  |  |  |  |  |
Intangible Assets, Gross (Excluding Goodwill) | 0.5 us-gaap_IntangibleAssetsGrossExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_OtherIntangibleAssetsMember / dei_LegalEntityAxis = wtm_TranzactMember | 0 us-gaap_IntangibleAssetsGrossExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_OtherIntangibleAssetsMember / dei_LegalEntityAxis = wtm_TranzactMember |  |  |  |
Amortization of Intangible Assets | 0 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_OtherIntangibleAssetsMember / dei_LegalEntityAxis = wtm_TranzactMember | 0 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_OtherIntangibleAssetsMember / dei_LegalEntityAxis = wtm_TranzactMember |  |  |  |
Intangible Assets, Net (Excluding Goodwill) | 0.5 us-gaap_IntangibleAssetsNetExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_OtherIntangibleAssetsMember / dei_LegalEntityAxis = wtm_TranzactMember | 0 us-gaap_IntangibleAssetsNetExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_OtherIntangibleAssetsMember / dei_LegalEntityAxis = wtm_TranzactMember |  |  |  |
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life | 7 years |  |  |  |  |
Other Intangible Assets [Member] | OneBeacon |  |  |  |  |  |
Goodwill [Line Items] |  |  |  |  |  |
Intangible Assets, Gross (Excluding Goodwill) | 9.4 us-gaap_IntangibleAssetsGrossExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_OtherIntangibleAssetsMember / dei_LegalEntityAxis = wtm_OnebeaconMember | 9.4 us-gaap_IntangibleAssetsGrossExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_OtherIntangibleAssetsMember / dei_LegalEntityAxis = wtm_OnebeaconMember |  |  |  |
Amortization of Intangible Assets | 5.7 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_OtherIntangibleAssetsMember / dei_LegalEntityAxis = wtm_OnebeaconMember | 4.3 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_OtherIntangibleAssetsMember / dei_LegalEntityAxis = wtm_OnebeaconMember |  |  |  |
Intangible Assets, Net (Excluding Goodwill) | 3.7 us-gaap_IntangibleAssetsNetExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_OtherIntangibleAssetsMember / dei_LegalEntityAxis = wtm_OnebeaconMember | 5.1 us-gaap_IntangibleAssetsNetExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_OtherIntangibleAssetsMember / dei_LegalEntityAxis = wtm_OnebeaconMember |  |  |  |
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life | 10 years |  |  |  |  |
Trade Names [Member] | Tranzact [Member] |  |  |  |  |  |
Goodwill [Line Items] |  |  |  |  |  |
Intangible Assets, Gross (Excluding Goodwill) | 25.6 us-gaap_IntangibleAssetsGrossExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_TradeNamesMember / dei_LegalEntityAxis = wtm_TranzactMember | 0 us-gaap_IntangibleAssetsGrossExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_TradeNamesMember / dei_LegalEntityAxis = wtm_TranzactMember |  |  |  |
Amortization of Intangible Assets | 0.9 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_TradeNamesMember / dei_LegalEntityAxis = wtm_TranzactMember | 0 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_TradeNamesMember / dei_LegalEntityAxis = wtm_TranzactMember |  |  |  |
Intangible Assets, Net (Excluding Goodwill) | 24.7 us-gaap_IntangibleAssetsNetExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_TradeNamesMember / dei_LegalEntityAxis = wtm_TranzactMember | 0 us-gaap_IntangibleAssetsNetExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_TradeNamesMember / dei_LegalEntityAxis = wtm_TranzactMember |  |  |  |
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life | 6 years |  |  |  |  |
Contract-Based Intangible Assets [Member] | Sirius Group |  |  |  |  |  |
Goodwill [Line Items] |  |  |  |  |  |
Intangible Assets, Gross (Excluding Goodwill) | 15.2 us-gaap_IntangibleAssetsGrossExcludingGoodwill / us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_ContractBasedIntangibleAssetsMember / dei_LegalEntityAxis = wtm_SiriusGroupMember | 15.6 us-gaap_IntangibleAssetsGrossExcludingGoodwill / us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_ContractBasedIntangibleAssetsMember / dei_LegalEntityAxis = wtm_SiriusGroupMember |  |  |  |
Amortization of Intangible Assets | 0 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_ContractBasedIntangibleAssetsMember / dei_LegalEntityAxis = wtm_SiriusGroupMember | 0 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_ContractBasedIntangibleAssetsMember / dei_LegalEntityAxis = wtm_SiriusGroupMember |  |  |  |
Intangible Assets, Net (Excluding Goodwill) | $ 15.2 us-gaap_IntangibleAssetsNetExcludingGoodwill / us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_ContractBasedIntangibleAssetsMember / dei_LegalEntityAxis = wtm_SiriusGroupMember | $ 15.6 us-gaap_IntangibleAssetsNetExcludingGoodwill / us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_ContractBasedIntangibleAssetsMember / dei_LegalEntityAxis = wtm_SiriusGroupMember |  |  |  |

X
- Definition Weighted average amortization period of finite-lived intangible assets acquired either individually or as part of a group of assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16265-109275 + Details
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X
- Definition Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16323-109275 + Details
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Period Type: | instant

X
- Definition Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=14024403&loc=d3e13816-109267 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266 + Details
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- Definition Amount before accumulated amortization of intangible assets, excluding goodwill. + References No definition available. + Details
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- Definition Sum of the carrying amounts of all intangible assets, excluding goodwill, as of the balance sheet date, net of accumulated amortization and impairment charges. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6388964&loc=d3e16212-109274 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph ((a)(1),(b)) -URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16323-109275 + Details
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- Definition Carrying amount of finite-lived intangible assets, indefinite-lived intangible assets and goodwill. Goodwill is an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. Intangible assets are assets, not including financial assets, lacking physical substance. + References No definition available. + Details
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- Definition Intangible Assets, Gross (Including Goodwill) + References No definition available. + Details
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