XML 85 R65.htm IDEA: XBRL DOCUMENT
v3.6.0.2

Reserves for Unpaid Losses and Loss Adjustment Expenses (Narrative) (Details) - USD ($) $ in Millions |  | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | --- | ---
Sep. 30, 2014 | Dec. 31, 2014 | Sep. 30, 2014 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Loss and Loss Adjustment Expense Reserve Activity |  |  |  |  |  |
Workers compensation discount percent |  |  |  | 2.50% | 2.50% |
Prior Accident Year |  |  |  | $ 14.8 | $ (4.0) | $ 92.0
Increase (decrease) in reserves |  |  |  | 664.0 | 708.9 | 824.0
Current Accident Year |  |  |  | 649.2 | 712.9 | 732.0
Workers compensation discount amount |  |  |  | 1.6 | 1.1 |
OneBeacon |  |  |  |  |  |
Loss and Loss Adjustment Expense Reserve Activity |  |  |  |  |  |
Prior Accident Year | $ 75.5 | $ 75.5 | $ 14.3 | 15.4 | (1.8) | 89.8
Increase (decrease) in reserves |  | 109.2 | 109.2 |  |  | 89.8
Current Accident Year |  | 33.7 | $ 33.7 |  |  |
Star & Shield Insurance Exchange [Member] |  |  |  |  |  |
Loss and Loss Adjustment Expense Reserve Activity |  |  |  |  |  |
Prior Accident Year |  |  |  | (0.6) | $ (2.2) | 2.2
OneBeacon |  |  |  |  |  |
Loss and Loss Adjustment Expense Reserve Activity |  |  |  |  |  |
Workers compensation discount amount |  |  |  | $ 1.6 |  |
Professional Insurance (1) | OneBeacon |  |  |  |  |  |
Loss and Loss Adjustment Expense Reserve Activity |  |  |  |  |  |
Prior Accident Year |  | 46.4 |  |  |  |
Increase (decrease) in reserves |  | 69.3 |  |  |  | 59.1
Current Accident Year |  | 22.9 |  |  |  |
Crop Business | OneBeacon |  |  |  |  |  |
Loss and Loss Adjustment Expense Reserve Activity |  |  |  |  |  |
Prior Accident Year |  | 0.0 |  |  |  |
Increase (decrease) in reserves |  | 3.8 |  |  |  | 0.0
Current Accident Year |  | 3.8 |  |  |  |
Specialty Products | OneBeacon |  |  |  |  |  |
Loss and Loss Adjustment Expense Reserve Activity |  |  |  |  |  |
Prior Accident Year |  | 51.7 |  |  |  |
Increase (decrease) in reserves |  | 80.1 |  |  |  | $ 61.8
Current Accident Year |  | 28.4 |  |  |  |
Management's estimate [Member] | Specialty Products | OneBeacon |  |  |  |  |  |
Loss and Loss Adjustment Expense Reserve Activity |  |  |  |  |  |
Current Accident Year |  | $ 29.9 |  |  |  |
Minimum | OneBeacon |  |  |  |  |  |
Loss and Loss Adjustment Expense Reserve Activity |  |  |  |  |  |
Years that Claims Close |  |  |  | 5 years |  |
Maximum | OneBeacon |  |  |  |  |  |
Loss and Loss Adjustment Expense Reserve Activity |  |  |  |  |  |
Years that Claims Close |  |  |  | 7 years |  |
Healthcare Sector [Member] | OneBeacon |  |  |  |  |  |
Loss and Loss Adjustment Expense Reserve Activity |  |  |  |  |  |
Prior Accident Year |  |  |  | $ 40.7 |  |
Technology Sector [Member] | OneBeacon |  |  |  |  |  |
Loss and Loss Adjustment Expense Reserve Activity |  |  |  |  |  |
Prior Accident Year |  |  |  | 9.3 |  |
Programs [Member] | OneBeacon |  |  |  |  |  |
Loss and Loss Adjustment Expense Reserve Activity |  |  |  |  |  |
Prior Accident Year |  |  |  | 13.3 |  |
Accident | OneBeacon |  |  |  |  |  |
Loss and Loss Adjustment Expense Reserve Activity |  |  |  |  |  |
Prior Accident Year |  |  |  | 16.1 |  |
Entertainment | OneBeacon |  |  |  |  |  |
Loss and Loss Adjustment Expense Reserve Activity |  |  |  |  |  |
Prior Accident Year |  |  |  | 9.4 |  |
Financial Services Sector | OneBeacon |  |  |  |  |  |
Loss and Loss Adjustment Expense Reserve Activity |  |  |  |  |  |
Prior Accident Year |  |  |  | $ 8.2 |  |

X
- Definition Amount, after effects of reinsurance, of increase (decrease) in the liability for unpaid claims and claims adjustment expense. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=65670824&loc=d3e14764-158437 + Details
Name: | us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpensePeriodIncreaseDecrease
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount, after effects of reinsurance, of expense for claims incurred in the current reporting period and related claims settlement costs. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=65670824&loc=d3e14764-158437 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 235 -Section S99 -Paragraph 3 -Subparagraph (SX 210.12-18) -URI http://asc.fasb.org/extlink&oid=34713774&loc=d3e575016-122915 + Details
Name: | us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount, after effects of reinsurance, of expense (reversal of expense) for claims incurred in prior reporting periods and related claims settlement costs. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=65670824&loc=d3e14764-158437 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 235 -Section S99 -Paragraph 3 -Subparagraph (SX 210.12-18) -URI http://asc.fasb.org/extlink&oid=34713774&loc=d3e575016-122915 + Details
Name: | us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Current year monetary amount of the change in worker's compensation reserve liability resulting from the discount applied to reduce the reserve to present value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.(a),13(b)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 + Details
Name: | us-gaap_WorkersCompensationDiscountAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Percent discount applied to worker's compensation reserve liability to reduce the reserve to present value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=6482852&loc=d3e14931-158439 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.13(b)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=65670824&loc=d3e14754-158437 + Details
Name: | us-gaap_WorkersCompensationDiscountPercent
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Asbestos and Environmental Loss and Loss Adjustment, Expense Reserves Activity + References No definition available. + Details
Name: | wtm_AsbestosAndEnvironmentalLossAndLossAdjustmentExpenseReservesActivityLineItems
Namespace Prefix: | wtm_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Years that Claims Close + References No definition available. + Details
Name: | wtm_YearsthatClaimsClose
Namespace Prefix: | wtm_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=wtm_OnebeaconMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=wtm_StarShieldInsuranceExchangeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=wtm_OnebeaconMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ProductOrServiceAxis=wtm_ProfessionalInsuranceMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ProductOrServiceAxis=wtm_CropinsuranceMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ProductOrServiceAxis=wtm_SpecialtyProductsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ChangeInAccountingEstimateByTypeAxis=wtm_ManagementsestimateMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RangeAxis=us-gaap_MinimumMember
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: |

X
- Details
Name: | us-gaap_NoncashOrPartNoncashDivestituresByUniqueNameAxis=us-gaap_HealthcareSectorMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_NoncashOrPartNoncashDivestituresByUniqueNameAxis=us-gaap_TechnologySectorMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_NoncashOrPartNoncashDivestituresByUniqueNameAxis=wtm_ProgramsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_NoncashOrPartNoncashDivestituresByUniqueNameAxis=wtm_AccidentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_NoncashOrPartNoncashDivestituresByUniqueNameAxis=wtm_EntertainmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_NoncashOrPartNoncashDivestituresByUniqueNameAxis=us-gaap_FinancialServicesSectorMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |