XML 99 R89.htm IDEA: XBRL DOCUMENT
v3.22.2

Employee Share-Based Incentive Compensation Plans - Narrative (Details) $ in Millions | 3 Months Ended | 6 Months Ended | 36 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | ---
Jun. 30, 2022 USD ($) shares | Jun. 30, 2021 USD ($) shares | Jun. 30, 2022 USD ($) shares | Jun. 30, 2021 USD ($) shares | Dec. 31, 2021 USD ($) shares | Mar. 31, 2022 USD ($) | Mar. 31, 2021 USD ($) | Dec. 31, 2020 USD ($)
Performance Share | W T M Incentive Plan |  |  |  |  |  |  |  |
Share-based compensation arrangement by share-based payment award |  |  |  |  |  |  |  |
Vesting period |  |  | 3 years |  |  |  |  |
Performance cycle period |  |  | 3 years |  |  |  |  |
New grants (in shares) | shares | 150 | 475 | 13,225 | 13,475 | 750 |  |  |
Additional compensation cost that would be recognized if all outstanding performance shares vested | $ | $ 44.0 |  | $ 44.0 |  |  |  |  |
Performance Share | Minimum | W T M Incentive Plan |  |  |  |  |  |  |  |
Share-based compensation arrangement by share-based payment award |  |  |  |  |  |  |  |
Share-based compensation arrangement by share-based payment award, multiplier |  |  | 0 |  |  |  |  |
Performance Share | Maximum | W T M Incentive Plan |  |  |  |  |  |  |  |
Share-based compensation arrangement by share-based payment award |  |  |  |  |  |  |  |
Share-based compensation arrangement by share-based payment award, multiplier |  |  | 2 |  |  |  |  |
Restricted Stock |  |  |  |  |  |  |  |
Share-based compensation arrangement by share-based payment award |  |  |  |  |  |  |  |
Vesting period |  |  | 34 months |  |  |  |  |
Restricted Stock | W T M Incentive Plan |  |  |  |  |  |  |  |
Share-based compensation arrangement by share-based payment award |  |  |  |  |  |  |  |
Additional compensation cost that would be recognized if all outstanding performance shares vested | $ | $ 23.0 | $ 23.2 | $ 23.0 | $ 23.2 | $ 15.9 | $ 26.5 | $ 26.2 | $ 15.2
Issued (in shares) | shares | 150 | 475 | 13,225 | 13,475 |  |  |  |

X
- Definition Amount of cost not yet recognized for nonvested award under share-based payment arrangement. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (i) -URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901 + Details
Name: | us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901 + Details
Name: | us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(01) -URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901 + Details
Name: | us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

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

X
- Definition Number of shares issued under share-based payment arrangement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901 + Details
Name: | us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the performance cycle on conclusion of which shares become payable. + References No definition available. + Details
Name: | wtm_ShareBasedCompensationArrangementByShareBasedPaymentAwardPerformanceCyclePeriod
Namespace Prefix: | wtm_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Share-based Compensation Arrangement by Share-based Payment Award, Multiplier for Determining Payout + References No definition available. + Details
Name: | wtm_SharebasedCompensationArrangementbySharebasedPaymentAwardMultiplierforDeterminingPayout
Namespace Prefix: | wtm_
Data Type: | xbrli:pureItemType
Balance Type: | na
Period Type: | duration

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

X
- Details
Name: | us-gaap_PlanNameAxis=wtm_WTMIncentivePlanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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