XML 46 R62.htm IDEA: XBRL DOCUMENT
v3.3.0.814

Investment Securities (Mortgage-backed Asset Securities Table) (Details) - USD ($) $ in Millions | Sep. 30, 2015 | Jun. 30, 2015 | Dec. 31, 2014 | Sep. 30, 2014 | Dec. 31, 2013
--- | --- | --- | --- | --- | ---
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |
Fair value investments | $ 3,365.4 |  | $ 3,343.6 | $ 3,610.7 | $ 3,889.0
Commercial Mortgage Backed Securities Fixed Rate [Member] |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |
Fair value investments | 93.2 |  |  |  |
Government National Mortgage Association Certificates and Obligations (GNMA) |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |
Fair value investments | 293.9 |  | 308.7 |  |
Federal National Mortgage Association Certificates and Obligations (FNMA) |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |
Fair value investments | 41.6 |  | 33.4 |  |
Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |
Fair value investments | 24.8 |  | 28.9 |  |
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |
Fair value investments | 360.3 |  | 371.0 |  |
Residential Mortgage Backed Securities |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |
Fair value investments | 123.7 |  | 71.0 |  |
Commercial Mortgage Backed Securities |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |
Fair value investments | 133.7 |  | 109.3 |  |
Mortgage-backed Securities, Issued by Private Enterprises |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |
Fair value investments | 257.4 |  | 180.3 |  |
Collateralized Mortgage Backed Securities |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |
Fair value investments | 617.7 |  | 551.3 |  |
Collateralized Credit Card Securities |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |
Fair value investments | 293.3 |  | 218.1 |  |
Collateralized Auto Loans |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |
Fair value investments | 276.4 |  | 152.8 |  |
Collateralized Securities, Other |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |
Fair value investments | 78.0 |  | 45.7 |  |
Asset-backed Securities, Securitized Loans and Receivables |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |
Fair value investments | 647.7 |  | 416.6 |  |
Mortgage-backed and asset-backed securities |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |
Fair value investments | 1,265.4 |  | 967.9 |  |
Level 2 Inputs |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |
Fair value investments | 2,561.6 |  | 2,372.9 | $ 2,495.9 | $ 2,575.4
Level 2 Inputs | Government National Mortgage Association Certificates and Obligations (GNMA) |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |
Fair value investments | 293.9 |  | 308.7 |  |
Level 2 Inputs | Federal National Mortgage Association Certificates and Obligations (FNMA) |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |
Fair value investments | 41.6 |  | 33.4 |  |
Level 2 Inputs | Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |
Fair value investments | 24.8 |  | 28.9 |  |
Level 2 Inputs | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |
Fair value investments | 360.3 |  | 371.0 |  |
Level 2 Inputs | Residential Mortgage Backed Securities |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |
Fair value investments | 123.7 |  | 71.0 |  |
Level 2 Inputs | Commercial Mortgage Backed Securities |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |
Fair value investments | 133.7 |  | 109.3 |  |
Level 2 Inputs | Mortgage-backed Securities, Issued by Private Enterprises |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |
Fair value investments | 257.4 |  | 180.3 |  |
Level 2 Inputs | Collateralized Mortgage Backed Securities |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |
Fair value investments | 617.7 |  | 551.3 |  |
Level 2 Inputs | Collateralized Credit Card Securities |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |
Fair value investments | 293.3 |  | 218.1 |  |
Level 2 Inputs | Collateralized Auto Loans |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |
Fair value investments | 276.4 |  | 152.8 |  |
Level 2 Inputs | Collateralized Securities, Other |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |
Fair value investments | 78.0 |  | 45.7 |  |
Level 2 Inputs | Asset-backed Securities, Securitized Loans and Receivables |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |
Fair value investments | 647.7 |  | 416.6 |  |
Level 2 Inputs | Mortgage-backed and asset-backed securities |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |
Fair value investments | 1,265.4 |  | 967.9 |  |
Level 3 Inputs | Government National Mortgage Association Certificates and Obligations (GNMA) |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |
Fair value investments | 0.0 |  | 0.0 |  |
Level 3 Inputs | Federal National Mortgage Association Certificates and Obligations (FNMA) |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |
Fair value investments | 0.0 |  | 0.0 |  |
Level 3 Inputs | Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |
Fair value investments | 0.0 |  | 0.0 |  |
Level 3 Inputs | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |
Fair value investments | 0.0 |  | 0.0 |  |
Level 3 Inputs | Residential Mortgage Backed Securities |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |
Fair value investments | 0.0 |  | 0.0 |  |
Level 3 Inputs | Commercial Mortgage Backed Securities |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |
Fair value investments | 0.0 |  | 0.0 |  |
Level 3 Inputs | Mortgage-backed Securities, Issued by Private Enterprises |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |
Fair value investments | 0.0 |  | 0.0 |  |
Level 3 Inputs | Collateralized Mortgage Backed Securities |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |
Fair value investments | 0.0 |  | 0.0 |  |
Level 3 Inputs | Collateralized Credit Card Securities |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |
Fair value investments | 0.0 |  | 0.0 |  |
Level 3 Inputs | Collateralized Auto Loans |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |
Fair value investments | 0.0 |  | 0.0 |  |
Level 3 Inputs | Collateralized Securities, Other |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |
Fair value investments | 0.0 |  | 0.0 |  |
Level 3 Inputs | Asset-backed Securities, Securitized Loans and Receivables |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |
Fair value investments | 0.0 |  | 0.0 |  |
Level 3 Inputs | Mortgage-backed and asset-backed securities |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |
Fair value investments | $ 0.0 |  | $ 0.0 |  |
Maximum | Commercial Mortgage Backed Securities |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |
Loans and Leases Receivable, Ratio of Nonperforming Loans to All Loans |  | 1.00% |  |  |

X
- Definition Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method. + References Reference 1: 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 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 35 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=27723805&loc=d3e24584-111560 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=51813488&loc=d3e22054-111558 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Available-for-Sale Securities -URI http://asc.fasb.org/extlink&oid=6505594 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 1 -Subparagraph a, f, g -Article 7 + Details
Name: | us-gaap_InvestmentsFairValueDisclosure
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Reflects the percentage derived from dividing impaired loans on which interest has ceased to be accrued by total loans. + References No definition available. + Details
Name: | us-gaap_LoansAndLeasesReceivableRatioOfNonperformingLoansToAllLoans
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
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_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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

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

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

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

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

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

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

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

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

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

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

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

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

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