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Third-Party Reinsurance | 12 Months Ended
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Dec. 31, 2025
Reinsurance Disclosures [Abstract] |
Third-Party Reinsurance | Third-Party Reinsurance Ark/WM Outrigger In the normal course of business, Ark may seek to limit losses that arise from catastrophes or other events by reinsuring certain risks with third-party reinsurers. Ark remains liable for risks reinsured in the event that the reinsurer does not honor its obligations under reinsurance contracts. The following table summarizes the effects of reinsurance on written and earned premiums and on loss and LAE for the Ark/WM Outrigger segment for the years ended December 31, 2025, 2024 and 2023.
|  | Year Ended December 31,
Millions |  | 2025 |  | 2024 |  | 2023
Written premiums: |  |  |  |  |  |
Direct |  | $ | 1,260.1 |  |  | $ | 1,101.5 |  |  | $ | 931.9 |
Assumed |  | 1,297.1 |  |  | 1,105.5 |  |  | 966.5 |
Gross written premiums |  | 2,557.2 |  |  | 2,207.0 |  |  | 1,898.4 |
Ceded (1) |  | (745.6) |  |  | (527.9) |  |  | (377.5) |
Net written premiums |  | $ | 1,811.6 |  |  | $ | 1,679.1 |  |  | $ | 1,520.9 |
Earned premiums: |  |  |  |  |  |
Direct |  | $ | 1,130.9 |  |  | $ | 1,004.2 |  |  | $ | 848.1 |
Assumed |  | 1,198.9 |  |  | 1,088.2 |  |  | 925.6 |
Gross earned premiums |  | 2,329.8 |  |  | 2,092.4 |  |  | 1,773.7 |
Ceded (2) |  | (632.4) |  |  | (504.6) |  |  | (364.0) |
Net earned premiums |  | $ | 1,697.4 |  |  | $ | 1,587.8 |  |  | $ | 1,409.7 |
Loss and LAE: |  |  |  |  |  |
Gross |  | $ | 1,118.6 |  |  | $ | 1,056.7 |  |  | $ | 782.5 |
Ceded (3) |  | (274.4) |  |  | (200.9) |  |  | (55.7) |
Net loss and LAE |  | $ | 844.2 |  |  | $ | 855.8 |  |  | $ | 726.8 |
(1) The years ended December 31, 2025, 2024 and 2023 exclude written premiums of $84.2, $86.5 and $110.0 ceded by Ark to WM Outrigger Re, which eliminate in White Mountains’s consolidated financial statements. (2) The years ended December 31, 2025, 2024 and 2023 exclude earned premiums of $84.6, $88.0 and $104.3 ceded by Ark to WM Outrigger Re, which eliminate in White Mountains’s consolidated financial statements. (3) The years ended December 31, 2025, 2024 and 2023 exclude loss and LAE of $25.4 and $29.9 and $15.6 ceded by Ark to WM Outrigger Re, which eliminate in White Mountains’s consolidated financial statements. The following table presents the Ark/WM Outrigger segment’s reinsurance recoverables as of December 31, 2025 and December 31, 2024:
Millions |  | December 31, 2025 |  | December 31, 2024
Reinsurance recoverables on unpaid losses (1) |  | $ | 508.3 |  |  | $ | 434.4 |
Reinsurance recoverables on paid losses (2) |  | 117.6 |  |  | 57.5 |
Ceded unearned premiums (3) |  | 210.2 |  |  | 97.1 |
Reinsurance recoverables |  | $ | 836.1 |  |  | $ | 589.0 |
(1) The reinsurance recoverables on unpaid losses exclude $29.5 and $31.8 ceded by Ark to WM Outrigger Re as of December 31, 2025 and 2024, which eliminate in White Mountains’s consolidated financial statements. (2) The reinsurance recoverables on paid losses exclude $5.2 and $3.1 ceded by Ark to WM Outrigger Re as of December 31, 2025 and 2024, which eliminates in White Mountains’s consolidated financial statements. (3) The ceded unearned premiums exclude $3.9 and $4.3 ceded by Ark to WM Outrigger Re as of December 31, 2025 and 2024, which eliminate in White Mountains’s consolidated financial statements. As reinsurance contracts do not relieve Ark of its obligation to its policyholders, Ark seeks to reduce the credit risk associated with reinsurance balances by avoiding over-reliance on specific reinsurers through the application of concentration limits and thresholds. Ark is selective with its reinsurers, placing reinsurance with only those reinsurers having a strong financial condition. Ark monitors the financial strength of its reinsurers on an ongoing basis. The following table presents the Ark/WM Outrigger segment’s gross and net reinsurance recoverables by the reinsurers’ A.M. Best Company, Inc (“A.M. Best”) ratings as of December 31, 2025:
$ in Millions |  | As of December 31, 2025
A.M. Best Rating (1) |  | Gross |  | Collateral |  | Net |  | % of Total
A+ or better |  | $ | 404.0 |  |  | $ | — |  |  | $ | 404.0 |  |  | 71.7 | %
A- to A |  | 147.7 |  | — |  |  | 147.7 |  | 26.2 |
B++ or lower and not rated |  | 74.2 | (2) | 62.3 | (2) | 11.9 |  | 2.1 |
Total |  | $ | 625.9 |  |  | $ | 62.3 |  |  | $ | 563.6 |  |  | 100.0 | %
(1) A.M. Best financial strength ratings as detailed above are: “A+ or better” (Superior) “A- to A” (Excellent), “B++” (Good). (2) Excludes $34.7 ceded by Ark to WM Outrigger Re as of December 31, 2025, which eliminates in White Mountains’s consolidated financial statements.

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