XML 148 R132.htm IDEA: XBRL DOCUMENT
v3.22.4

Variable Interest Entities (Details) $ in Millions |  |  | 3 Months Ended | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | --- | ---
May 07, 2020 USD ($) | Jan. 24, 2018 USD ($) | Dec. 31, 2022 USD ($) | Dec. 31, 2022 USD ($) director | Dec. 31, 2021 USD ($) | May 06, 2020 | May 31, 2019 USD ($)
Private equity funds |  |  |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |  |  |
Trading security, fair value |  |  | $ 140.6 | $ 140.6 | $ 141.8 |  |
Outrigger Re |  |  |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |  |  |
Purchase price |  |  | $ 205.0 |  |  |  |
Ownership interest after all transactions (as a percent) |  |  | 100.00% |  |  |  |
BAM |  |  |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |  |  |
Number directors to designate for election | director |  |  |  | 2 |  |  |
First Loss Reinsurance Treaty | HG Global |  |  |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |  |  |
Percentage of par value of policy reinsured |  |  | 15.00% | 15.00% |  |  |
First Loss Reinsurance Treaty | BAM |  |  |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |  |  |
Percentage of premiums |  |  | 60.00% | 60.00% |  |  |
Elementum Holdings, L.P. |  |  |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |  |  |
Ownership interest (as a percent) |  |  | 29.70% | 29.70% | 29.70% |  | 30.00%
Other investments |  |  | $ 30.0 | $ 30.0 |  |  | $ 55.1
DavidShield |  |  |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |  |  |
Ownership interest (as a percent) |  | 50.00% |  |  |  |  |
PassportCard |  |  |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |  |  |
Ownership interest (as a percent) |  | 50.00% |  |  |  |  |
PassportCard/DavidShield |  |  |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |  |  |
Ownership interest (as a percent) | 53.80% |  | 53.80% | 53.80% | 53.80% | 50.00% |
Other investments |  |  | $ 144.6 | $ 144.6 |  |  |
Payments to acquire businesses, gross |  | $ 41.8 |  |  |  |  |
Payments to acquire business |  | $ 28.3 |  |  |  |  |
Additional investment in acquisition | $ 15.0 |  |  |  |  |  |

X
- Definition Amount of consideration transferred in asset acquisition. Includes, but is not limited to, cash, liability incurred by acquirer, and equity interest issued by acquirer. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 50 -Section 30 -Paragraph 2 -URI https://asc.fasb.org/extlink&oid=126928898&loc=d3e9215-128498 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 50 -Section 55 -Paragraph 1 -URI https://asc.fasb.org/extlink&oid=6829253&loc=SL6831962-166255 Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 50 -Section 25 -Paragraph 1 -URI https://asc.fasb.org/extlink&oid=127000608&loc=d3e9135-128495 Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 50 -Section 30 -Paragraph 1 -URI https://asc.fasb.org/extlink&oid=126928898&loc=d3e9212-128498 + Details
Name: | us-gaap_AssetAcquisitionConsiderationTransferred
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a)(1) -URI https://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571 + Details
Name: | us-gaap_EquityMethodInvestmentOwnershipPercentage
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Amount of investments classified as other. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(12)) -URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.1(f,g)) -URI https://asc.fasb.org/extlink&oid=126734703&loc=d3e572229-122910 + Details
Name: | us-gaap_OtherInvestments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The cash outflow associated with the acquisition of business during the period. The cash portion only of the acquisition price. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (b)(1) -URI https://asc.fasb.org/extlink&oid=126975305&loc=d3e6927-128479 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 13 -Subparagraph (b) -URI https://asc.fasb.org/extlink&oid=126954810&loc=d3e3213-108585 + Details
Name: | us-gaap_PaymentsToAcquireBusinessesGross
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The cash outflow associated with the acquisition of a business, net of the cash acquired from the purchase. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 13 -Subparagraph (b) -URI https://asc.fasb.org/extlink&oid=126954810&loc=d3e3213-108585 + Details
Name: | us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Value of stock issued pursuant to acquisitions during the period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 2 -URI https://asc.fasb.org/extlink&oid=126973232&loc=d3e21463-112644 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI https://asc.fasb.org/extlink&oid=120397183&loc=d3e187085-122770 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.29-31) -URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
Name: | us-gaap_StockIssuedDuringPeriodValueAcquisitions
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Percentage of subsidiary's or equity method investee's stock owned by parent immediately after all stock transactions. + References No definition available. + Details
Name: | us-gaap_SubsidiaryOrEquityMethodInvesteeCumulativePercentageOwnershipAfterAllTransactions
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:percentItemType
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_VariableInterestEntityLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage of par value of policy reinsured. + References No definition available. + Details
Name: | wtm_PercentageOfParValueOfPolicyReinsured
Namespace Prefix: | wtm_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Percentage of Premiums + References No definition available. + Details
Name: | wtm_PercentageofPremiums
Namespace Prefix: | wtm_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the number of directors who can be elected to the board by the holders of the preference shares, subject to certain specified conditions. + References No definition available. + Details
Name: | wtm_RightToElectDirectorsOnBoardNumber
Namespace Prefix: | wtm_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Trading Security, Fair Value + References No definition available. + Details
Name: | wtm_TradingSecurityFairValue
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_InvestmentTypeAxis=us-gaap_PrivateEquityFundsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_AssetAcquisitionAxis=wtm_OutriggerReMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

X
- Details
Name: | us-gaap_TransactionTypeAxis=wtm_FirstLossReinsuranceTreatyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=wtm_ElementumHoldingsL.P.Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=wtm_DavidShieldMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=wtm_PassportCardMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=wtm_DavidShieldPassportCardMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |