XML 87 R69.htm IDEA: XBRL DOCUMENT
v3.7.0.1

Investment Securities (Significant Unobservable Inputs) (Details) $ in Millions | 3 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Mar. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) | Dec. 31, 2015 input
Standard & Poor's, AAA Rating | Non-Agency Residential Mortgage [Member] | Broker Pricing [Member] |  |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |  |
Assets, Fair Value Disclosure | $ 58.3 |  |
Fair Value Measurements, Valuation Techniques | 102.56 |  |
NR | Private equity funds | Discounted cash flows |  |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |  |
Assets, Fair Value Disclosure | $ 22.1 | $ 22.1 |
Fair Value Measurements, Valuation Techniques | 0.25 | 0.25 |
NR | Private equity funds | Option pricing method [Member] |  |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |  |
Assets, Fair Value Disclosure | $ 9.4 | $ 9.3 |
Fair Value Measurements, Valuation Techniques | 0.21 | 0.21 |
NR | Convertible Preferred Stock | Multiple of EBITA [Member] |  |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |  |
Assets, Fair Value Disclosure | $ 3.7 | $ 3.6 |
Unobservable Inputs | input |  |  | 0
Fair Value Measurements, Valuation Techniques | 6 | 6.0 |
NR | Community Reinvestment Vehicle [Member] | GAAP net equity [Member] |  |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |  |
Assets, Fair Value Disclosure | $ 14.5 | $ 14.3 |
Fair Value Measurements, Valuation Techniques | 14.5 | 14.3 |
NR | Seller Priority Surplus Note [Member] | Discounted cash flows |  |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |  |
Assets, Fair Value Disclosure | $ 48.1 | $ 51.1 |
Fair Value Measurements, Valuation Techniques | 0.106 | 0.096 |
NR | Pari Passu Surplus Note [Member] | Discounted cash flows |  |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |  |
Assets, Fair Value Disclosure | $ 21.5 | $ 20.8 |
Fair Value Measurements, Valuation Techniques | 0.150 | 0.15 |
Investment A [Member] | NR | Private equity funds | Recent transaction [Member] |  |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |  |
Assets, Fair Value Disclosure | $ 21.0 | $ 21.0 |
Fair Value Measurements, Valuation Techniques | 1 | 1.00 |
Investment B [Member] | NR | Private equity funds | Recent transaction [Member] |  |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |  |
Assets, Fair Value Disclosure | $ 3.4 | $ 3.2 |
Fair Value Measurements, Valuation Techniques | 2.521 | 2.52 |
Investment E [Member] | NR | Convertible Preferred Stock | Recent transaction [Member] |  |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |  |
Assets, Fair Value Disclosure | $ 27.0 | $ 27.0 |
Fair Value Measurements, Valuation Techniques | 3.83 | 3.83 |
Investment C | NR | Private equity funds |  |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |  |
Time Until Expiration of Security | 4 years | 4 years |
Volatility Rate | 50.00% | 50.00% |
Risk Free Rate | 1.00% | 1.00% |
Standard & Poor's, B Rating [Member] |  |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |  |
Basis points | 4.00% | 2.50% |
Standard & Poor's, CCC Rating [Member] |  |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |  |
Basis points | 4.00% | 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=66048111&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=66048111&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 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 Unobservable Inputs + References No definition available. + Details
Name: | wtm_UnobservableInputs
Namespace Prefix: | wtm_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | instant

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=us-gaap_StandardPoorsAAARatingMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

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

X
- Details
Name: | invest_CreditRatingSourceAxis=wtm_StandardPoorsNrRatingMember
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_DiscountedCashFlowValuationTechniqueMember
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_FairValueByAssetClassAxis=us-gaap_ConvertiblePreferredStockMember
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=wtm_CommunityReinvestmentVehicleMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ValuationTechniqueAxis=wtm_GAAPnetequityMember
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: | invest_InvestmentAxis=wtm_InvestmentAMember
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: | invest_InvestmentAxis=wtm_InvestmentBMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | invest_InvestmentAxis=wtm_InvestmentEMember
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_CreditRatingStandardPoorsAxis=us-gaap_StandardPoorsBRatingMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_CreditRatingStandardPoorsAxis=us-gaap_StandardPoorsCCCRatingMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |