XML 81 R71.htm IDEA: XBRL DOCUMENT
v3.22.2.2

Goodwill and Other Intangible Assets - Summary of the Acquisition Date Fair Values of Goodwill and Other Intangible Assets (Details) $ in Millions | Sep. 30, 2022 USD ($)
--- | ---
Ark |
Acquired Finite-Lived Intangible Assets [Line Items] |
Goodwill and intangible assets acquired | $ 292.5
Other |
Acquired Finite-Lived Intangible Assets [Line Items] |
Goodwill and intangible assets acquired | $ 86.6

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

X
- Definition Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Goodwill and Intangible Assets + References No definition available. + Details
Name: | wtm_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedGoodwillandIntangibleAssets
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_BusinessAcquisitionAxis=wtm_ArkInsuranceHoldingsLimitedMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_BusinessAcquisitionAxis=wtm_OtherOperationsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |