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v3.20.2

Segment Information - Financial Information for White Mountain's Segments (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2020 | Sep. 30, 2019 | Sep. 30, 2020 | Sep. 30, 2019
Segment Reporting Information [Line Items] |  |  |  |
Earned insurance premiums | $ 6.2 | $ 5.2 | $ 17.2 | $ 13.7
Net investment income | 71.2 | 18.4 | 113.7 | 55.4
Net realized and unrealized investment gains | 306.6 | 67.0 | 302.8 | 233.1
Realized gain and unrealized investment gain from the MediaAlpha Transaction |  |  |  | 182.2
Advertising and commission revenues | 60.3 | 51.3 | 180.3 | 200.9
Other revenues | 15.2 | 13.6 | 45.9 | 32.8
Total revenues | 459.5 | 155.5 | 659.9 | 718.1
Insurance acquisition expenses | 1.6 | 1.4 | 5.4 | 4.1
Other underwriting expenses | 0.1 | 0.1 | 0.3 | 0.3
Cost of sales | 2.3 | 2.3 | 6.5 | 45.6
General and administrative expenses | 103.3 | 78.0 | 266.7 | 236.9
Broker commission expenses | 17.1 | 15.3 | 56.4 | 48.9
Change in fair value of contingent consideration earnout liabilities | 0.7 | (2.0) | (1.6) | 5.6
Amortization of other intangible assets | 5.4 | 4.6 | 17.1 | 15.4
Interest expense | 7.8 | 4.7 | 21.2 | 12.7
Total expenses | 138.3 | 104.4 | 372.0 | 369.5
Pre-tax income (loss) from continuing operations | 321.2 | 51.1 | 287.9 | 348.6
HG Global/ BAM |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Earned insurance premiums | 6.2 | 5.2 | 17.2 | 13.7
Net investment income | 4.7 | 5.4 | 15.1 | 16.1
Net realized and unrealized investment gains | 3.2 | 7.1 | 23.7 | 30.4
Realized gain and unrealized investment gain from the MediaAlpha Transaction |  |  |  | 0.0
Advertising and commission revenues | 0.0 | 0.0 | 0.0 | 0.0
Other revenues | 0.4 | 0.3 | 2.1 | 1.3
Total revenues | 14.5 | 18.0 | 58.1 | 61.5
Insurance acquisition expenses | 1.6 | 1.4 | 5.4 | 4.1
Other underwriting expenses | 0.1 | 0.1 | 0.3 | 0.3
Cost of sales | 0.0 | 0.0 | 0.0 | 0.0
General and administrative expenses | 13.9 | 12.5 | 41.1 | 39.1
Broker commission expenses | 0.0 | 0.0 | 0.0 | 0.0
Change in fair value of contingent consideration earnout liabilities | 0.0 | 0.0 | 0.0 | 0.0
Amortization of other intangible assets | 0.0 | 0.0 | 0.0 | 0.0
Interest expense | 0.0 | 0.0 | 0.0 | 0.0
Total expenses | 15.6 | 14.0 | 46.8 | 43.5
Pre-tax income (loss) from continuing operations | (1.1) | 4.0 | 11.3 | 18.0
NSM |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Earned insurance premiums | 0.0 | 0.0 | 0.0 | 0.0
Net investment income | 0.0 | 0.0 | 0.0 | 0.0
Net realized and unrealized investment gains | 0.0 | 0.0 | 0.0 | 0.0
Realized gain and unrealized investment gain from the MediaAlpha Transaction |  |  |  | 0.0
Advertising and commission revenues | 58.2 | 49.4 | 174.2 | 147.6
Other revenues | 12.5 | 10.5 | 37.6 | 27.7
Total revenues | 70.7 | 59.9 | 211.8 | 175.3
Insurance acquisition expenses | 0.0 | 0.0 |  | 0.0
Other underwriting expenses | 0.0 | 0.0 | 0.0 | 0.0
Cost of sales | 0.0 | 0.0 | 0.0 | 0.0
General and administrative expenses | 42.9 | 33.3 | 131.0 | 91.4
Broker commission expenses | 17.1 | 15.3 | 56.4 | 48.9
Change in fair value of contingent consideration earnout liabilities | 0.7 | (2.0) | (1.6) | 5.6
Amortization of other intangible assets | 5.1 | 4.4 | 16.2 | 13.5
Interest expense | 6.1 | 4.4 | 16.1 | 12.2
Total expenses | 71.9 | 55.4 | 218.1 | 171.6
Pre-tax income (loss) from continuing operations | (1.2) | 4.5 | (6.3) | 3.7
Kudu |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Earned insurance premiums | 0.0 | 0.0 | 0.0 | 0.0
Net investment income | 6.4 | 4.6 | 19.3 | 8.6
Net realized and unrealized investment gains | 9.8 | 2.7 | 1.5 | 3.1
Realized gain and unrealized investment gain from the MediaAlpha Transaction |  |  |  | 0.0
Advertising and commission revenues | 0.0 | 0.0 | 0.0 | 0.0
Other revenues | 0.1 | 0.2 | 0.2 | 0.2
Total revenues | 16.3 | 7.5 | 21.0 | 11.9
Insurance acquisition expenses | 0.0 | 0.0 | 0.0 | 0.0
Other underwriting expenses | 0.0 | 0.0 | 0.0 | 0.0
Cost of sales | 0.0 | 0.0 | 0.0 | 0.0
General and administrative expenses | 2.2 | 4.5 | 7.5 | 6.7
Broker commission expenses | 0.0 | 0.0 | 0.0 | 0.0
Change in fair value of contingent consideration earnout liabilities | 0.0 | 0.0 | 0.0 | 0.0
Amortization of other intangible assets | 0.1 | 0.2 | 0.3 | 0.2
Interest expense | 1.4 | 0.0 | 4.3 | 0.0
Total expenses | 3.7 | 4.7 | 12.1 | 6.9
Pre-tax income (loss) from continuing operations | 12.6 | 2.8 | 8.9 | 5.0
MediaAlpha |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Earned insurance premiums |  |  |  | 0.0
Net investment income |  |  |  | 0.0
Net realized and unrealized investment gains |  |  |  | 0.0
Realized gain and unrealized investment gain from the MediaAlpha Transaction |  |  |  | 0.0
Advertising and commission revenues | 0.0 | 0.0 | 0.0 | 48.8
Other revenues |  |  |  | 0.0
Total revenues | 0.0 | 0.0 | 0.0 | 48.8
Insurance acquisition expenses |  |  |  | 0.0
Other underwriting expenses |  |  |  | 0.0
Cost of sales | 0.0 | 0.0 | 0.0 | 40.6
General and administrative expenses | 0.0 | 0.0 | 0.0 | 12.5
Broker commission expenses |  |  |  | 0.0
Change in fair value of contingent consideration earnout liabilities |  |  |  | 0.0
Amortization of other intangible assets | 0.0 | 0.0 | 0.0 | 1.6
Interest expense | 0.0 | 0.0 | 0.0 | 0.2
Total expenses | 0.0 | 0.0 | 0.0 | 54.9
Pre-tax income (loss) from continuing operations |  |  |  | (6.1)
Other Operations |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Earned insurance premiums | 0.0 | 0.0 | 0.0 | 0.0
Net investment income | 60.1 | 8.4 | 79.3 | 30.7
Net realized and unrealized investment gains | 293.6 | 57.2 | 277.6 | 199.6
Realized gain and unrealized investment gain from the MediaAlpha Transaction | 0.0 | 0.0 | 0.0 | 182.2
Advertising and commission revenues | 2.1 | 1.9 | 6.1 | 4.5
Other revenues | 2.2 | 2.6 | 6.0 | 3.6
Total revenues | 358.0 | 70.1 | 369.0 | 420.6
Insurance acquisition expenses | 0.0 | 0.0 | 0.0 | 0.0
Other underwriting expenses | 0.0 | 0.0 | 0.0 | 0.0
Cost of sales | 2.3 | 2.3 | 6.5 | 5.0
General and administrative expenses | 44.3 | 27.7 | 87.1 | 87.2
Broker commission expenses | 0.0 | 0.0 | 0.0 | 0.0
Change in fair value of contingent consideration earnout liabilities | 0.0 | 0.0 | 0.0 | 0.0
Amortization of other intangible assets | 0.2 | 0.0 | 0.6 | 0.1
Interest expense | 0.3 | 0.3 | 0.8 | 0.3
Total expenses | 47.1 | 30.3 | 95.0 | 92.6
Pre-tax income (loss) from continuing operations | $ 310.9 | $ 39.8 | $ 274.0 | $ 328.0

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

X
- Definition Broker Commission Expense + References No definition available. + Details
Name: | wtm_BrokerCommissionExpense
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Commission Revenue + References No definition available. + Details
Name: | wtm_CommissionRevenue
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Realized and Unrealized Gains from Transaction + References No definition available. + Details
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Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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

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

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

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

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