XML 127 R110.htm IDEA: XBRL DOCUMENT
v3.25.0.1

Employee Share-Based Incentive Compensation Plans - Performance Shares (Details) - USD ($) $ in Millions | 1 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2024 | Mar. 31, 2023 | Mar. 31, 2022 | Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Target Performance Shares Outstanding |  |  |  |  |  |
Beginning of period (in shares) |  |  |  | 37,031 | 39,449 | 40,828
Shares paid or expired (in shares) |  |  |  | (13,475) | (13,350) | (14,625)
Grants in period (in shares) |  |  |  | 11,405 | 10,895 | 13,225
Forfeitures and cancellations (in shares) |  |  |  | (102) | 37 | 21
End of period (in shares) |  |  |  | 34,859 | 37,031 | 39,449
Accrued Expense |  |  |  |  |  |
Beginning of period |  |  |  | $ 69.4 | $ 67.5 | $ 42.2
Shares paid or expired |  |  |  | (44.9) | (40.8) | (26.4)
New grants |  |  |  | 0.0 | 0.0 | 0.0
Forfeitures and cancellations |  |  |  | 0.0 | (0.1) | (0.4)
Expense recognized |  |  |  | 46.6 | 42.8 | 52.1
End of period |  |  |  | $ 71.1 | $ 69.4 | $ 67.5
Performance Shares |  |  |  |  |  |
Accrued Expense |  |  |  |  |  |
Percentage of target payout - minimum actual | 188.00% | 200.00% | 172.00% |  |  |

X
- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. + References No definition available. + Details
Name: | us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- References No definition available. + Details
Name: | wtm_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantDateFairValueRollForward
Namespace Prefix: | wtm_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the percentage of target achieved, low end of range. + References No definition available. + Details
Name: | wtm_ShareBasedCompensationArrangementByShareBasedPaymentAwardPercentageOfTargetAchievedPayout
Namespace Prefix: | wtm_
Data Type: | dtr-types1:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Share-based Compensation Arrangement by Share-based Payment Award, Performance Shares + References No definition available. + Details
Name: | wtm_ShareBasedCompensationArrangementByShareBasedPaymentAwardPerformanceShares
Namespace Prefix: | wtm_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

X
- Definition Share-based Compensation Arrangement by Share-based Payment Award, Performance Shares, Accrued Liability + References No definition available. + Details
Name: | wtm_ShareBasedCompensationArrangementByShareBasedPaymentAwardPerformanceSharesAccruedLiability
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Share-based Compensation Arrangement by Share-based Payment Award, Performance Shares, Accrued Liability, Expense In Period + References No definition available. + Details
Name: | wtm_ShareBasedCompensationArrangementByShareBasedPaymentAwardPerformanceSharesAccruedLiabilityExpenseInPeriod
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Share-based Compensation Arrangement by Share-based Payment Award, Performance Shares, Accrued Liability, Forfeited and Cancelled In Period + References No definition available. + Details
Name: | wtm_ShareBasedCompensationArrangementByShareBasedPaymentAwardPerformanceSharesAccruedLiabilityForfeitedAndCancelledInPeriod
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Share-based Compensation Arrangement by Share-based Payment Award, Performance Shares, Accrued Liability, Grants In Period + References No definition available. + Details
Name: | wtm_ShareBasedCompensationArrangementByShareBasedPaymentAwardPerformanceSharesAccruedLiabilityGrantsInPeriod
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The amount of performance shares that were paid out (including deposits into a deferred compensation plan) or that expired due to failure to meet performance criteria. + References No definition available. + Details
Name: | wtm_ShareBasedCompensationArrangementByShareBasedPaymentAwardPerformanceSharesAccruedLiabilitySharesPaidInPeriod
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Share-Based Compensation Arrangement by Share-Based Payment Award, Performance Shares, Forfeited and Cancelled In Period + References No definition available. + Details
Name: | wtm_ShareBasedCompensationArrangementByShareBasedPaymentAwardPerformanceSharesForfeitedAndCancelledInPeriod
Namespace Prefix: | wtm_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

X
- Definition Share-based Compensation Arrangement by Share-based Payment Award, Performance Shares, Grants In Period + References No definition available. + Details
Name: | wtm_ShareBasedCompensationArrangementByShareBasedPaymentAwardPerformanceSharesGrantsInPeriod
Namespace Prefix: | wtm_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

X
- Definition The number of target performance shares that were paid out (including deposits into a deferred compensation plan) or that expired due to failure to meet performance criteria. + References No definition available. + Details
Name: | wtm_ShareBasedCompensationArrangementByShareBasedPaymentAwardPerformanceSharesSharesPaidInPeriod
Namespace Prefix: | wtm_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_AwardTypeAxis=us-gaap_PerformanceSharesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |