XML 91 R81.htm IDEA: XBRL DOCUMENT
v3.22.2.2

Derivatives (Details) - HG Global - Interest Rate Cap - USD ($) |  | 3 Months Ended | 9 Months Ended
--- | --- | --- | ---
Jun. 16, 2022 | Sep. 30, 2022 | Sep. 30, 2022
Derivative [Line Items] |  |  |
Notional amount | $ 150,000,000 |  |
Premiums paid | $ 3,300,000 |  |
Derivative, fair value, net |  | $ 3,900,000 | $ 3,900,000
Interest Expense |  |  |
Derivative [Line Items] |  |  |
Change in fair value of derivative instruments |  | $ 2,100,000 | $ 600,000
Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate |  |  |
Derivative [Line Items] |  |  |
Derivative, cap interest rate | 3.50% |  |
3-month variable rate |  | 3.60% | 3.60%

X
- Definition Cap rate on an interest rate derivative such as an interest rate cap or collar. If market rates exceed the cap rate, a payment or receipt is triggered on the contract. + References No definition available. + Details
Name: | us-gaap_DerivativeCapInterestRate
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition The premium (cost) of a hedge, expensed during the period. + References No definition available. + Details
Name: | us-gaap_DerivativeCostOfHedge
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Fair value of the assets less the liabilities of a derivative or group of derivatives. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -URI https://asc.fasb.org/extlink&oid=123594938&loc=d3e13433-108611 + Details
Name: | us-gaap_DerivativeFairValueOfDerivativeNet
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_DerivativeLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Nominal or face amount used to calculate payment on derivative. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 1B -URI https://asc.fasb.org/extlink&oid=125515794&loc=SL5580258-113959 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 1A -Subparagraph (d) -URI https://asc.fasb.org/extlink&oid=125515794&loc=SL5579245-113959 + Details
Name: | us-gaap_DerivativeNotionalAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | instant

X
- Definition Amount, after tax and reclassification, of gain (loss) from derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 11 -URI https://asc.fasb.org/extlink&oid=126968391&loc=d3e637-108580 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (d) -URI https://asc.fasb.org/extlink&oid=126968391&loc=SL7669646-108580 + Details
Name: | us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition 3-month Variable Rate + References No definition available. + Details
Name: | wtm_A3MonthVariableRate
Namespace Prefix: | wtm_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

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

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

X
- Details
Name: | us-gaap_IncomeStatementLocationAxis=us-gaap_InterestExpenseMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_VariableRateAxis=us-gaap_SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |