XML 137 R120.htm IDEA: XBRL DOCUMENT
v3.22.0.1

Employee Share-Based Incentive Compensation Plans - Narrative (Details) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2021 USD ($) multiplier shares | Dec. 31, 2020 USD ($) shares | Dec. 31, 2019 USD ($) shares | Dec. 31, 2018 USD ($)
Performance Shares |  |  |  |
Share-based compensation arrangement by share-based payment award |  |  |  |
Vesting period | 3 years |  |  |
Multiplier for determining payout, low end of range | multiplier | 0 |  |  |
Multiplier for determining payout, high end of range | multiplier | 2 |  |  |
Performance cycle period | 3 years |  |  |
Unamortized grant date fair value | $ | $ 12.0 |  |  |
Performance Shares | 2021 – 2023 |  |  |  |
Share-based compensation arrangement by share-based payment award |  |  |  |
Targeted performance goal (as a percent) | 8.00% |  |  |
Payout for maximum growth target percentage | 200.00% |  |  |
Performance Shares | 2019 – 2021 |  |  |  |
Share-based compensation arrangement by share-based payment award |  |  |  |
Targeted performance goal (as a percent) | 7.00% |  |  |
Payout for maximum growth target percentage | 200.00% |  |  |
Performance Shares | 2020 – 2022 |  |  |  |
Share-based compensation arrangement by share-based payment award |  |  |  |
Targeted performance goal (as a percent) | 7.00% |  |  |
Payout for maximum growth target percentage | 200.00% |  |  |
Performance Shares | Minimum | 2021 – 2023 |  |  |  |
Share-based compensation arrangement by share-based payment award |  |  |  |
Payout for minimum growth target percentage | 3.00% |  |  |
Performance Shares | Minimum | 2019 – 2021 |  |  |  |
Share-based compensation arrangement by share-based payment award |  |  |  |
Payout for minimum growth target percentage | 2.00% |  |  |
Performance Shares | Minimum | 2020 – 2022 |  |  |  |
Share-based compensation arrangement by share-based payment award |  |  |  |
Payout for minimum growth target percentage | 2.00% |  |  |
Performance Shares | Maximum | 2021 – 2023 |  |  |  |
Share-based compensation arrangement by share-based payment award |  |  |  |
Payout for minimum growth target percentage | 13.00% |  |  |
Performance Shares | Maximum | 2019 – 2021 |  |  |  |
Share-based compensation arrangement by share-based payment award |  |  |  |
Payout for minimum growth target percentage | 12.00% |  |  |
Performance Shares | Maximum | 2020 – 2022 |  |  |  |
Share-based compensation arrangement by share-based payment award |  |  |  |
Payout for minimum growth target percentage | 12.00% |  |  |
Range Of Performance Cycle From 2021 to 2023 | W T M Incentive and Phantom Plan |  |  |  |
Share-based compensation arrangement by share-based payment award |  |  |  |
Performance shares (in shares) | 13,475 |  |  |
Restricted Share Cliff Vesting in January 2023 | W T M Incentive and Phantom Plan |  |  |  |
Share-based compensation arrangement by share-based payment award |  |  |  |
Performance shares (in shares) |  | 14,055 |  |
Restricted Share Cliff Vesting in January 2022 | W T M Incentive and Phantom Plan |  |  |  |
Share-based compensation arrangement by share-based payment award |  |  |  |
Performance shares (in shares) |  |  | 15,600 |
Restricted Stock |  |  |  |
Share-based compensation arrangement by share-based payment award |  |  |  |
Vesting period | 3 years |  |  |
Performance shares (in shares) | 13,475 | 14,055 | 15,600 |
Unamortized grant date fair value | $ | $ 15.9 | $ 15.2 | $ 16.7 | $ 12.5
Restricted Share Cliff Vesting in January 2024 | W T M Incentive and Phantom Plan |  |  |  |
Share-based compensation arrangement by share-based payment award |  |  |  |
Performance shares (in shares) | 13,475 |  |  |

X
- Definition Amount of cost not yet recognized for nonvested award 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 -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=120381028&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://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
Name: | us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
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 http://asc.fasb.org/extlink&oid=120381028&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 high end of the range of multiplier for number of shares initially granted to determine payout. + References No definition available. + Details
Name: | wtm_ShareBasedCompensationArrangementByShareBasedPaymentAwardMultiplierForDeterminingPayoutHighEndOfRange
Namespace Prefix: | wtm_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the low end of the range of the multiplier for the number of shares initially granted to determine payout. + References No definition available. + Details
Name: | wtm_ShareBasedCompensationArrangementByShareBasedPaymentAwardMultiplierForDeterminingPayoutLowEndOfRange
Namespace Prefix: | wtm_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the percentage of target achieved, high end of range. + References No definition available. + Details
Name: | wtm_ShareBasedCompensationArrangementByShareBasedPaymentAwardPayoutForMaximumGrowthTargetPercentage
Namespace Prefix: | wtm_
Data Type: | dtr-types:percentItemType
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 Represents the percentage growth in intrinsic business value per share to achieve payment. + References No definition available. + Details
Name: | wtm_SharebasedCompensationArrangementbySharebasedPaymentAwardPerformanceGoalPercentageforPayout
Namespace Prefix: | wtm_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Share-based Compensation Arrangement by Share-based Payment Award, Targeted Performance Goal for Personnel Expressed as Percentage of Growth in Intrinsic Business Value + References No definition available. + Details
Name: | wtm_SharebasedCompensationArrangementbySharebasedPaymentAwardTargetedPerformanceGoalforPersonnelExpressedasPercentageofGrowthinIntrinsicBusinessValue
Namespace Prefix: | wtm_
Data Type: | dtr-types:percentItemType
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: | wtm_ShareBasedCompensationArrangementByPerformanceSharesAwardPerformanceCycleAxis=wtm_PerformanceCycleRange1Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | wtm_ShareBasedCompensationArrangementByPerformanceSharesAwardPerformanceCycleAxis=wtm_PerformanceCycleRange3Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | wtm_ShareBasedCompensationArrangementByPerformanceSharesAwardPerformanceCycleAxis=wtm_PerformanceCycleRange2Member
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=wtm_RangeOfPerformanceCycleFrom2021To2023Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

X
- Details
Name: | us-gaap_AwardTypeAxis=wtm_RestrictedShareCliffVestingInJanuary2023Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_AwardTypeAxis=wtm_RestrictedShareCliffVestinginJanuary2022Member
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: |

X
- Details
Name: | us-gaap_AwardTypeAxis=wtm_RestrictedShareCliffVestingInJanuary2024Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |