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Loss and Loss Adjustment Expense Reserves - TPC Participation (Details) | Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
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Syndicate - Ark Insurance Holdings Limited |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |
Percent of underwriting capital provided by third parties | 0.00% | 42.80% | 58.30%

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- 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
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- Definition Reinsurance, Loss and Loss Reserves, Participation Results, Percentage + References No definition available. + Details
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Namespace Prefix: | wtm_
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Balance Type: | na
Period Type: | instant

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- Details
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Namespace Prefix: |
Data Type: | na
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