XML 113 R93.htm IDEA: XBRL DOCUMENT
v3.3.1.900

Investment Securities (Significant Unobservable Inputs) (Details) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2015 USD ($) Investment | Dec. 31, 2014 USD ($) Investment
Quantitative information for Level 3 Fair Value Measurements Assets |  |
Fair Value, Assets Measured on Recurring Basis, Transfers out | $ 41.8 | $ 53.0
Number of Investments with Significant Unobseravble Inputs | Investment | 1 | 1
Standard Poors NR Rating [Member] | Redeemable preferred stocks | Par Value [Member] |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |
Assets, Fair Value Disclosure | $ 70.0 |
Standard Poors NR Rating [Member] | Redeemable preferred stocks | Discounted cash flows |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |
Assets, Fair Value Disclosure |  | $ 71.1
Standard Poors NR Rating [Member] | Redeemable preferred stocks | Discount Yield |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |
Unobservable Inputs | 70.0 | .07065
Standard Poors NR Rating [Member] | Private equity funds | Multiple of GAAP book value [Member] |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |
Assets, Fair Value Disclosure |  | $ 39.5
Standard Poors NR Rating [Member] | Private equity funds | Recent transaction [Member] |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |
Assets, Fair Value Disclosure | $ 21.0 |
Standard Poors NR Rating [Member] | Private equity securities | Multiple of GAAP book value |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |
Unobservable Inputs |  | 290.96
Standard Poors NR Rating [Member] | Private equity securities | Recent transaction [Member] |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |
Assets, Fair Value Disclosure | $ 5.7 |
Standard Poors NR Rating [Member] | Private equity securities | Multiple of EBITDA [Member] |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |
Unobservable Inputs | 6.0 | 6
Assets, Fair Value Disclosure |  | $ 3.8
Standard Poors NR Rating [Member] | Fixed maturity investments | Discounted cash flows |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |
Assets, Fair Value Disclosure |  | $ 5.3
Standard Poors NR Rating [Member] | Fixed maturity investments | Discount Yield [Member] |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |
Unobservable Inputs |  | .10
Standard Poors NR Rating [Member] | Seller Priority Surplus Note [Member] | Discounted cash flows |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |
Timing of Interest Payments | 5 years | 5 years
Unobservable Inputs | 0.13 |
Assets, Fair Value Disclosure |  | $ 44.0
Timing of principal payments | 10 years | 10 years
Standard Poors NR Rating [Member] | Seller Priority Surplus Note [Member] | Discount Yield [Member] |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |
Unobservable Inputs |  | 0.093
Standard Poors NR Rating [Member] | Pari Passu Surplus Note [Member] | Discounted cash flows |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |
Timing of Interest Payments | 5 years |
Unobservable Inputs | 0.224 |
Assets, Fair Value Disclosure | $ 13.5 | $ 21.1
Timing of principal payments | 10 years | 10 years
Standard Poors NR Rating [Member] | Pari Passu Surplus Note [Member] | Discount Yield [Member] |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |
Unobservable Inputs |  | 0.135
Level 2 |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |
Fair Value, Assets Measured on Recurring Basis, Transfers out | $ 0.0 | $ 0.0
Level 3 Inputs | Fixed maturity investments |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |
Fair Value, Assets Measured on Recurring Basis, Transfers out | $ 40.6 | $ 52.8
Ironshore [Member] | Standard Poors NR Rating [Member] | Private equity funds | Multiple of GAAP book value |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |
Unobservable Inputs |  | 1.10
PassportCard [Member] | Standard Poors NR Rating [Member] | Private equity funds | Multiple of GAAP book value |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |
Unobservable Inputs | 1.00 |
Surplus Note |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |
RBC Score | 250.00% |
durchblicker.at [Member] | Standard Poors NR Rating [Member] | Private equity funds | Recent transaction [Member] |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |
Assets, Fair Value Disclosure |  | $ 20.1
durchblicker.at [Member] | Standard Poors NR Rating [Member] | Private equity funds | Recent Transaction Two [Member] |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |
Unobservable Inputs | 1.03 | 1.06
Assets, Fair Value Disclosure | $ 33.8 |
Captricity [Member] | Standard Poors NR Rating [Member] | Private equity securities | Recent transaction [Member] |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |
Unobservable Inputs | 3.83 |
Assets, Fair Value Disclosure | $ 27.0 |
durchblicker.at [Member] | Standard Poors NR Rating [Member] | Private equity funds | Option pricing method [Member] |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |
Assets, Fair Value Disclosure | $ 9.6 |
durchblicker.at [Member] | Standard Poors NR Rating [Member] | Private equity funds | Recent Transaction Three [Member] |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |
Assets, Fair Value Disclosure |  | $ 10.4
TaClaro [Member] | Standard Poors NR Rating [Member] | Private equity securities | Recent transaction [Member] |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |
Unobservable Inputs |  | .71
Assets, Fair Value Disclosure |  | $ 4.5
BE Reinsurance [Member] | Standard Poors NR Rating [Member] | Private equity funds |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |
Average Share Price Used As Unobservable Input | 4 years |
Volatility Rate | 60.00% |
Risk Free Rate | 1.15% |
Pari Passu Surplus Note [Member] |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |
basis points | 2.50% | 2.50%
Seller Priority Surplus Note [Member] |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |
basis points | 2.50% | 2.50%

X
- Definition Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258 + Details
Name: | us-gaap_AssetsFairValueDisclosure
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_FairValueInputsAssetsQuantitativeInformationLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Description of the inputs and valuation technique(s) used to measure fair value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (bbb) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258 + Details
Name: | us-gaap_FairValueMeasurementsValuationTechniques
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition basis points + References No definition available. + Details
Name: | wtm_Basispoints
Namespace Prefix: | wtm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition This element represents transfers out of one of the levels in the fair value hierarchy for assets measured at fair value on a recurring basis. + References No definition available. + Details
Name: | wtm_FairValueAssetsMeasuredOnRecurringBasisTransfersOut
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Number of Investments with Significant Unobseravble Inputs + References No definition available. + Details
Name: | wtm_NumberOfInvestmentsWithSignificantUnobseravbleInputs
Namespace Prefix: | wtm_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition RBC Score + References No definition available. + Details
Name: | wtm_RBCScore
Namespace Prefix: | wtm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Risk Free Rate + References No definition available. + Details
Name: | wtm_RiskFreeRate
Namespace Prefix: | wtm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Time Until Expiration of Security + References No definition available. + Details
Name: | wtm_TimeUntilExpirationofSecurity
Namespace Prefix: | wtm_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Timing of interest payments + References No definition available. + Details
Name: | wtm_Timingofinterestpayments
Namespace Prefix: | wtm_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Timing of principal payments + References No definition available. + Details
Name: | wtm_Timingofprincipalpayments
Namespace Prefix: | wtm_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Volatility Rate + References No definition available. + Details
Name: | wtm_VolatilityRate
Namespace Prefix: | wtm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | invest_CreditRatingSourceAxis=wtm_StandardPoorsNrRatingMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=us-gaap_PreferredStockMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ValuationTechniqueAxis=wtm_ParValueMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ValuationTechniqueAxis=wtm_DiscountedCashFlowValuationTechniqueMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ValuationTechniqueAxis=wtm_IssuersintenttocallMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=us-gaap_PrivateEquityFundsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ValuationTechniqueAxis=wtm_MultipleOfGaapBookValueMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ValuationTechniqueAxis=wtm_RecenttransactionMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=us-gaap_ConvertiblePreferredStockMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ValuationTechniqueAxis=wtm_AverageSharePriceMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ValuationTechniqueAxis=wtm_MultipleofEBITDAMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=us-gaap_DebtSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ValuationTechniqueAxis=wtm_DiscountYieldMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=wtm_SellerPrioritySurplusNoteMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=wtm_PariPassuSurplusNoteMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_FixedMaturitiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | invest_InvestmentAxis=wtm_IronshoreMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | invest_InvestmentAxis=wtm_PassportCardMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | invest_InvestmentAxis=wtm_SurplusNoteMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | invest_InvestmentAxis=wtm_Compare.comMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ValuationTechniqueAxis=wtm_RecentTransactionTwoMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | invest_InvestmentAxis=wtm_CaptricityMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | invest_InvestmentAxis=wtm_Durchblicker.atMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ValuationTechniqueAxis=wtm_OptionpricingmethodMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ValuationTechniqueAxis=wtm_RecentTransactionThreeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | invest_InvestmentAxis=wtm_TaClaroMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | invest_InvestmentAxis=wtm_BEReinsuranceMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=wtm_PariPassuSurplusNoteMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=wtm_SellerPrioritySurplusNoteMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |