XML 180 R81.htm IDEA: XBRL DOCUMENT
v3.22.1

Debt - Schedule of Weighted Average Interest Rates (Details) - USD ($) $ in Millions | 3 Months Ended
--- | ---
Mar. 31, 2022 | Mar. 31, 2021
Debt Instrument |  |
Interest expense | $ 9.0 | $ 13.1
Specialty Insurance Distribution (NSM) |  |
Debt Instrument |  |
Weighted Average | 273.5 | 277.4
Interest expense | $ 2.0 | $ 5.9
Weighted Average Interest rate | 2.90% | 8.50%
Specialty Insurance Distribution (NSM) | Revolving credit loan |  |
Debt Instrument |  |
Interest expense | $ 0.1 |
Specialty Insurance Distribution (NSM) | Interest Rate Swap and Interest Rate Cap |  |
Debt Instrument |  |
Interest expense | (2.7) | $ 0.6
Specialty Insurance Distribution (NSM) | Other Debt |  |
Debt Instrument |  |
Interest expense | 0.5 | 0.3
Specialty Insurance Distribution (NSM) | Term loan - hedged |  |
Debt Instrument |  |
Weighted Average | 0.0 | 147.6
Interest expense | $ 0.0 | $ 3.4
Weighted Average Interest rate | 0.00% | 9.20%
Specialty Insurance Distribution (NSM) | Term loan - unhedged |  |
Debt Instrument |  |
Weighted Average | $ 273.5 | $ 129.8
Interest expense | $ 2.0 | $ 2.5
Weighted Average Interest rate | 2.90% | 7.70%

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_DebtInstrumentLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Weighted average interest rate of debt outstanding. + References No definition available. + Details
Name: | us-gaap_DebtWeightedAverageInterestRate
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Amount of the cost of borrowed funds accounted for as interest expense for debt. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 6 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=120520924&loc=SL6036836-161870 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.8) -URI http://asc.fasb.org/extlink&oid=120395209&loc=SL114868664-224227 + Details
Name: | us-gaap_InterestExpenseDebt
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Long-Term Debt, Average Amount Outstanding + References No definition available. + Details
Name: | wtm_LongTermDebtAverageAmountOutstanding
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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

X
- Details
Name: | us-gaap_LongtermDebtTypeAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DerivativeInstrumentRiskAxis=wtm_InterestRateSwapAndInterestRateCapMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=wtm_OtherDebtMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_HedgingDesignationAxis=us-gaap_DesignatedAsHedgingInstrumentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_HedgingDesignationAxis=us-gaap_NondesignatedMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |