XML 91 R74.htm IDEA: XBRL DOCUMENT
v3.24.0.1

Goodwill and Other Intangible Assets - Summary of Goodwill and Intangible Assets (Details) - USD ($) $ in Millions | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Goodwill [Line Items] |  |  |
Goodwill | $ 168.8 | $ 176.5 | $ 142.3
Indefinite-lived intangible assets | 175.7 |  |
Other intangible assets, accumulated amortization | 17.0 | 12.2 |
Other intangible assets, finite-lived, net carrying value | 26.1 |  |
Total other intangible assets | 218.8 | 228.1 |
Total other intangible assets | 201.8 | 215.9 | 198.2
Total goodwill and other intangible assets | 387.6 | 404.6 |
Goodwill and other intangible assets | 370.6 | 392.4 | $ 340.5
Other Operations |  |  |
Goodwill [Line Items] |  |  |
Goodwill | 44.4 | 52.1 |
Other intangible assets, finite-lived, acquisition date fair value | 40.9 | 50.2 |
Other intangible assets, accumulated amortization | 15.5 | 11.0 |
Other intangible assets, finite-lived, net carrying value | 25.4 | 39.2 |
Goodwill and other intangible assets | 69.8 | 91.3 |
Ark/WM Outrigger | Operating Segments |  |  |
Goodwill [Line Items] |  |  |
Goodwill and other intangible assets | 292.5 | 292.5 |
Ark/WM Outrigger | Operating Segments | Ark |  |  |
Goodwill [Line Items] |  |  |
Goodwill | 116.8 | 116.8 |
Ark/WM Outrigger | Operating Segments | Ark | Underwriting Capacity |  |  |
Goodwill [Line Items] |  |  |
Indefinite-lived intangible assets | 175.7 | 175.7 |
Kudu | Operating Segments |  |  |
Goodwill [Line Items] |  |  |
Goodwill | 7.6 | 7.6 |
Goodwill and other intangible assets | $ 8.3 | 8.6 |
Trade names | Other Operations |  |  |
Goodwill [Line Items] |  |  |
Acquired other intangible assets, weighted average useful life (in years) | 13 years 3 months 18 days |  |
Other intangible assets, finite-lived, acquisition date fair value | $ 13.3 | 17.9 |
Other intangible assets, accumulated amortization | 4.1 | 3.0 |
Other intangible assets, finite-lived, net carrying value | $ 9.2 | 14.9 |
Trade names | Kudu | Operating Segments |  |  |
Goodwill [Line Items] |  |  |
Acquired other intangible assets, weighted average useful life (in years) | 7 years |  |
Other intangible assets, finite-lived, acquisition date fair value | $ 2.2 | 2.2 |
Other intangible assets, accumulated amortization | 1.5 | 1.2 |
Other intangible assets, finite-lived, net carrying value | $ 0.7 | 1.0 |
Customer relationships | Other Operations |  |  |
Goodwill [Line Items] |  |  |
Acquired other intangible assets, weighted average useful life (in years) | 10 years 10 months 24 days |  |
Other intangible assets, finite-lived, acquisition date fair value | $ 24.8 | 29.5 |
Other intangible assets, accumulated amortization | 10.3 | 7.5 |
Other intangible assets, finite-lived, net carrying value | 14.5 | 22.0 |
Total other intangible assets |  |  |
Goodwill [Line Items] |  |  |
Other intangible assets, accumulated amortization | 17.0 | 12.2 |
Total other intangible assets | $ 201.8 | 215.9 |
Total other intangible assets | Other Operations |  |  |
Goodwill [Line Items] |  |  |
Acquired other intangible assets, weighted average useful life (in years) | 12 years 1 month 6 days |  |
Other intangible assets, finite-lived, acquisition date fair value | $ 2.8 | 2.8 |
Other intangible assets, accumulated amortization | 1.1 | 0.5 |
Other intangible assets, finite-lived, net carrying value | $ 1.7 | $ 2.3 |

X
- Definition Weighted average amortization period of finite-lived intangible assets acquired either individually or as part of a group of assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 350 -SubTopic 30 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (a)(3) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482665/350-30-50-1 + Details
Name: | us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 210 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(16)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 350 -SubTopic 30 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (a)(1) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482665/350-30-50-2 + Details
Name: | us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount before amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 928 -SubTopic 340 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org//1943274/2147483147/928-340-50-1 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 350 -SubTopic 30 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (a)(1) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482665/350-30-50-2 + Details
Name: | us-gaap_FiniteLivedIntangibleAssetsGross
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount after amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 926 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Publisher FASB -URI https://asc.fasb.org//1943274/2147483154/926-20-50-5 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 350 -SubTopic 30 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (a)(1) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482665/350-30-50-2 + Details
Name: | us-gaap_FiniteLivedIntangibleAssetsNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 852 -SubTopic 10 -Name Accounting Standards Codification -Section 55 -Paragraph 10 -Publisher FASB -URI https://asc.fasb.org//1943274/2147481372/852-10-55-10 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Topic 350 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 24 -Publisher FASB -URI https://asc.fasb.org//1943274/2147482548/350-20-55-24 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 210 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(15)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 350 -SubTopic 20 -Name Accounting Standards Codification -Section 45 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org//1943274/2147482598/350-20-45-1 Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 350 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482573/350-20-50-1 Reference 6: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 350 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (h) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482573/350-20-50-1 Reference 7: http://www.xbrl.org/2003/role/disclosureRef -Topic 942 -SubTopic 210 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(10)(1)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147479853/942-210-S99-1 + Details
Name: | us-gaap_Goodwill
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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 Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 350 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org//1943274/2147482573/350-20-50-1 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Topic 350 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 24 -Publisher FASB -URI https://asc.fasb.org//1943274/2147482548/350-20-55-24 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 350 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482573/350-20-50-1 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 350 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482573/350-20-50-1 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 350 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482573/350-20-50-1 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Topic 350 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482573/350-20-50-1 Reference 7: http://www.xbrl.org/2003/role/disclosureRef -Topic 350 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (e) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482573/350-20-50-1 Reference 8: http://www.xbrl.org/2003/role/disclosureRef -Topic 350 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (f) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482573/350-20-50-1 Reference 9: http://www.xbrl.org/2003/role/disclosureRef -Topic 350 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (g) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482573/350-20-50-1 Reference 10: http://www.xbrl.org/2003/role/disclosureRef -Topic 350 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (h) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482573/350-20-50-1 Reference 11: http://www.xbrl.org/2003/role/disclosureRef -Topic 350 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1A -Publisher FASB -URI https://asc.fasb.org//1943274/2147482573/350-20-50-1A Reference 12: http://www.xbrl.org/2003/role/disclosureRef -Topic 350 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482573/350-20-50-2 + Details
Name: | us-gaap_GoodwillLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of assets, excluding financial assets and goodwill, lacking physical substance and having a projected indefinite period of benefit. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 350 -SubTopic 30 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482665/350-30-50-2 + Details
Name: | us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount before accumulated amortization of intangible assets, excluding goodwill. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 210 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(15)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1 + Details
Name: | us-gaap_IntangibleAssetsGrossExcludingGoodwill
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Sum of the carrying amounts of all intangible assets, excluding goodwill, as of the balance sheet date, net of accumulated amortization and impairment charges. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph ((a)(1),(b)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482665/350-30-50-2 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 45 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org//1943274/2147482686/350-30-45-1 + Details
Name: | us-gaap_IntangibleAssetsNetExcludingGoodwill
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Carrying amount of finite-lived intangible assets, indefinite-lived intangible assets and goodwill. Goodwill is an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. Intangible assets are assets, not including financial assets, lacking physical substance. + References No definition available. + Details
Name: | us-gaap_IntangibleAssetsNetIncludingGoodwill
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Intangible Assets, Gross (Including Goodwill) + References No definition available. + Details
Name: | wtm_IntangibleAssetsGrossIncludingGoodwill
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | srt_ConsolidationItemsAxis=us-gaap_CorporateNonSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

X
- Details
Name: | srt_ConsolidationItemsAxis=us-gaap_OperatingSegmentsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_SubsegmentsAxis=wtm_ArkInsuranceHoldingsLimitedSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis=wtm_UnderwritingCapacityMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

X
- Details
Name: | us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_TradeNamesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_CustomerRelationshipsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_OtherIntangibleAssetsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |