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Fair Value (Tables) | 12 Months Ended
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Dec. 31, 2025
Fair Value Disclosures [Abstract] |
Fair Values of Financial Instruments | The estimated fair values of the financial instruments were as follows:
|  | December 31, 2025 |  |  | December 31, 2024 |
|  | Carrying |  |  | Fair |  |  | Carrying |  |  | Fair |
(in millions) |  | Value |  |  | Value |  |  | Value |  |  | Value |
Financial Assets carried at: |  |  |  |  |  |  |  |  |  |  |  |
Fair Value through Accumulated Other Comprehensive Loss: |  |  |  |  |  |  |  |  |  |  |  |
Fixed maturities |  | $ | 9,536.5 |  |  | $ | 9,536.5 |  |  | $ | 8,542.2 |  |  | $ | 8,542.2 |
Fair Value through Net Income: |  |  |  |  |  |  |  |  |  |  |  |
Equity securities |  |  | 184.8 |  |  |  | 184.8 |  |  |  | 157.7 |  |  |  | 157.7 |
Other investments |  |  | 80.9 |  |  |  | 80.9 |  |  |  | 86.9 |  |  |  | 86.9 |
Amortized Cost/Cost: |  |  |  |  |  |  |  |  |  |  |  |
Other investments |  |  | 282.8 |  |  |  | 274.5 |  |  |  | 343.7 |  |  |  | 324.2 |
Cash and cash equivalents |  |  | 1,122.7 |  |  |  | 1,122.7 |  |  |  | 435.5 |  |  |  | 435.5 |
Total financial instruments |  | $ | 11,207.7 |  |  | $ | 11,199.4 |  |  | $ | 9,566.0 |  |  | $ | 9,546.5 |
Financial Liabilities carried at: |  |  |  |  |  |  |  |  |  |  |  |
Amortized Cost: |  |  |  |  |  |  |  |  |  |  |  |
Debt |  | $ | 1,218.3 |  |  | $ | 1,206.6 |  |  | $ | 784.1 |  |  | $ | 744.4 |
Fair Value, Investment Assets Measured on Recurring Basis | The following tables provide, for each hierarchy level, the Company’s investment assets that were measured at fair value on a recurring basis.
|  | DECEMBER 31, 2025 |
(in millions) |  | Total |  |  | Level 1 |  |  | Level 2 |  |  | Level 3 |
Fixed maturities: |  |  |  |  |  |  |  |  |  |  |  |
U.S. Treasury and government agencies |  | $ | 455.5 |  |  | $ | 331.1 |  |  | $ | 124.4 |  |  | $ | — |
Foreign governments |  |  | 2.7 |  |  |  | — |  |  |  | 2.7 |  |  |  | — |
Municipals |  |  | 847.7 |  |  |  | — |  |  |  | 840.3 |  |  |  | 7.4 |
Corporates |  |  | 4,253.5 |  |  |  | — |  |  |  | 4,253.5 |  |  |  | — |
Residential mortgage-backed, U.S. agency backed |  |  | 1,903.2 |  |  |  | — |  |  |  | 1,903.2 |  |  |  | — |
Residential mortgage-backed, non-agency |  |  | 518.6 |  |  |  | — |  |  |  | 518.6 |  |  |  | — |
Commercial mortgage-backed |  |  | 589.9 |  |  |  | — |  |  |  | 585.0 |  |  |  | 4.9 |
Other asset-backed |  |  | 965.4 |  |  |  | — |  |  |  | 965.4 |  |  |  | — |
Total fixed maturities |  |  | 9,536.5 |  |  |  | 331.1 |  |  |  | 9,193.1 |  |  |  | 12.3 |
Equity securities |  |  | 184.8 |  |  |  | 164.3 |  |  |  | — |  |  |  | 20.5 |
Other investments |  |  | 16.8 |  |  |  | — |  |  |  | 13.4 |  |  |  | 3.4 |
Total investment assets at fair value |  | $ | 9,738.1 |  |  | $ | 495.4 |  |  | $ | 9,206.5 |  |  | $ | 36.2 |
|  | DECEMBER 31, 2024 |
(in millions) |  | Total |  |  | Level 1 |  |  | Level 2 |  |  | Level 3 |
Fixed maturities: |  |  |  |  |  |  |  |  |  |  |  |
U.S. Treasury and government agencies |  | $ | 494.2 |  |  | $ | 363.9 |  |  | $ | 130.3 |  |  | $ | — |
Foreign governments |  |  | 1.9 |  |  |  | — |  |  |  | 1.9 |  |  |  | — |
Municipals |  |  | 893.8 |  |  |  | — |  |  |  | 886.2 |  |  |  | 7.6 |
Corporates |  |  | 3,805.9 |  |  |  | — |  |  |  | 3,805.9 |  |  |  | — |
Residential mortgage-backed, U.S. agency backed |  |  | 1,790.7 |  |  |  | — |  |  |  | 1,790.7 |  |  |  | — |
Residential mortgage-backed, non-agency |  |  | 333.4 |  |  |  | — |  |  |  | 333.4 |  |  |  | — |
Commercial mortgage-backed |  |  | 522.2 |  |  |  | — |  |  |  | 516.3 |  |  |  | 5.9 |
Other asset-backed |  |  | 700.1 |  |  |  | — |  |  |  | 700.1 |  |  |  | — |
Total fixed maturities |  |  | 8,542.2 |  |  |  | 363.9 |  |  |  | 8,164.8 |  |  |  | 13.5 |
Equity securities |  |  | 157.7 |  |  |  | 136.9 |  |  |  | — |  |  |  | 20.8 |
Other investments |  |  | 3.9 |  |  |  | — |  |  |  | — |  |  |  | 3.9 |
Total investment assets at fair value |  | $ | 8,703.8 |  |  | $ | 500.8 |  |  | $ | 8,164.8 |  |  | $ | 38.2 |
Estimated Fair Values of Financial Instruments Not Carried at Fair Value | The following tables provide, for each hierarchy level, the Company’s estimated fair values of financial instruments that were not carried at fair value.
|  | DECEMBER 31, 2025 |
(in millions) |  | Total |  |  | Level 1 |  |  | Level 2 |  |  | Level 3 |
Assets: |  |  |  |  |  |  |  |  |  |  |  |
Cash and cash equivalents |  | $ | 1,122.7 |  |  | $ | 1,122.7 |  |  | $ | — |  |  | $ | — |
Other investments |  |  | 274.5 |  |  |  | — |  |  |  | 6.1 |  |  |  | 268.4 |
Total financial instruments |  | $ | 1,397.2 |  |  | $ | 1,122.7 |  |  | $ | 6.1 |  |  | $ | 268.4 |
Liabilities: |  |  |  |  |  |  |  |  |  |  |  |
Debt |  | $ | 1,206.6 |  |  | $ | — |  |  | $ | 1,206.6 |  |  | $ | — |
|  | DECEMBER 31, 2024 |
(in millions) |  | Total |  |  | Level 1 |  |  | Level 2 |  |  | Level 3 |
Assets: |  |  |  |  |  |  |  |  |  |  |  |
Cash and cash equivalents |  | $ | 435.5 |  |  | $ | 435.5 |  |  | $ | — |  |  | $ | — |
Other investments |  |  | 324.2 |  |  |  | — |  |  |  | 6.1 |  |  |  | 318.1 |
Total financial instruments |  | $ | 759.7 |  |  | $ | 435.5 |  |  | $ | 6.1 |  |  | $ | 318.1 |
Liabilities: |  |  |  |  |  |  |  |  |  |  |  |
Debt |  | $ | 744.4 |  |  | $ | — |  |  | $ | 744.4 |  |  | $ | — |
Fair Value on Recurring Basis Using Significant Unobservable Inputs (Level 3) | The following tables provide a reconciliation for all assets measured at fair value on a recurring basis using significant unobservable inputs (Level 3).
YEAR ENDED DECEMBER 31, 2025 |  | Fixed Maturities |  |  |  |  |  |  |
(in millions) |  | Municipals |  |  | Corporates |  |  | Commercial mortgage- backed |  |  | Total |  |  | Equities and Other |  |  | Total Assets |
Balance at beginning of year |  | $ | 7.6 |  |  | $ | — |  |  | $ | 5.9 |  |  | $ | 13.5 |  |  | $ | 24.7 |  |  | $ | 38.2 |
Total gains: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Included in net realized and unrealized investment gains (losses) |  |  | — |  |  |  | — |  |  |  | — |  |  |  | — |  |  |  | 0.5 |  |  |  | 0.5 |
Included in other comprehensive income - changes in net unrealized gains on investment securities |  |  | 0.3 |  |  |  | — |  |  |  | 0.3 |  |  |  | 0.6 |  |  |  | — |  |  |  | 0.6 |
Settlements |  |  | (0.5 | ) |  |  | — |  |  |  | (1.3 | ) |  |  | (1.8 | ) |  |  | (1.3 | ) |  |  | (3.1 | )
Balance at end of year |  | $ | 7.4 |  |  | $ | — |  |  | $ | 4.9 |  |  | $ | 12.3 |  |  | $ | 23.9 |  |  | $ | 36.2 |
Changes in net unrealized gains for the period included in other comprehensive income for assets held at the end of the year |  | $ | 0.3 |  |  | $ | — |  |  | $ | 0.3 |  |  | $ | 0.6 |  |  | $ | — |  |  | $ | 0.6 |
YEAR ENDED DECEMBER 31, 2024 |  | Fixed Maturities |  |  |  |  |  |  |
(in millions) |  | Municipals |  |  | Corporates |  |  | Commercial mortgage- backed |  |  | Total |  |  | Equities and Other |  |  | Total Assets |
Balance at beginning of year |  | $ | 8.6 |  |  | $ | 0.1 |  |  | $ | 7.0 |  |  | $ | 15.7 |  |  | $ | 11.4 |  |  | $ | 27.1 |
Transfers out of Level 3 |  |  | — |  |  |  | (0.1 | ) |  |  | — |  |  |  | (0.1 | ) |  |  | — |  |  |  | (0.1 | )
Total gains (losses): |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Included in net realized and unrealized investment gains (losses) |  |  | — |  |  |  | — |  |  |  | — |  |  |  | — |  |  |  | 0.6 |  |  |  | 0.6 |
Included in other comprehensive income - changes in net unrealized gains on investment securities |  |  | — |  |  |  | — |  |  |  | (0.5 | ) |  |  | (0.5 | ) |  |  | — |  |  |  | (0.5 | )
Purchases and sales: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Addition |  |  | — |  |  |  | — |  |  |  | — |  |  |  | — |  |  |  | 14.2 |  |  |  | 14.2 |
Settlements |  |  | (1.0 | ) |  |  | — |  |  |  | (0.6 | ) |  |  | (1.6 | ) |  |  | (1.5 | ) |  |  | (3.1 | )
Balance at end of year |  | $ | 7.6 |  |  | $ | — |  |  | $ | 5.9 |  |  | $ | 13.5 |  |  | $ | 24.7 |  |  | $ | 38.2 |
Changes in net unrealized gains for the period included in other comprehensive income for assets held at the end of the year |  | $ | — |  |  | $ | — |  |  | $ | (0.5 | ) |  | $ | (0.5 | ) |  | $ | — |  |  | $ | (0.5 | )
There were no securities transferred between Level 2 and Level 3, d
Schedule of Additional Information About Significant Unobservable Inputs Used in Fair Valuations of Level 3 | The following table provides quantitative information about the significant unobservable inputs used by the Company in the fair value measurements of Level 3 assets. A valuation of $11.7 million for an equity security based on a dealer quote for which there was a lack of transparency as to inputs used to develop the valuation has been excluded.
DECEMBER 31 |  | 2025 |  | 2024
|  | Valuation |  | Significant |  | Fair |  |  | Range |  | Fair |  |  | Range
(in millions) |  | Technique |  | Unobservable Inputs |  | Value |  |  | (Wtd Average) |  | Value |  |  | (Wtd Average)
Fixed maturities: |  |  |  |  |  |  |  |  |  |  |  |  |  |
Municipals |  | Discounted |  | Discount for: |  | $ | 7.4 |  |  |  |  | $ | 7.6 |  |  |
|  | cash flow |  | Small issue size |  |  |  |  | 6.8 - 6.8% |  |  |  |  | 6.1 - 6.8% (6.7%)
Commercial mortgage-backed |  | Discounted cash flow |  | Discount for: Small issue size Above-market coupon Lease structure |  |  | 4.9 |  |  | 5.0% (5.0%) ― 0.3% (0.3%) |  |  | 5.9 |  |  | 3.0 - 5.0% (4.7%) 0.5% (0.5%) 0.3% (0.3%)
Equity securities |  | Market comparables |  | Net tangible asset |  |  | 1.5 |  |  | N/A |  |  | 1.4 |  |  | N/A
|  | Internal price based on |  | Discount for: |  |  | 7.3 |  |  |  |  |  | 7.4 |  |  |
|  | financing round |  | Market liquidity |  |  |  |  | 27.0% (27.0%) |  |  |  |  | 27.0% (27.0%)
Other |  | Discounted cash flow |  | Discount rate |  |  | 3.4 |  |  | 18.6% (18.6%) |  |  | 3.9 |  |  | 16.6% (16.6%)

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