Schedule III - Supplementary Insurance Information (Details) - USD ($) $ in Millions |
12 Months Ended | |||||
|---|---|---|---|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
Dec. 31, 2022 |
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| SEC Schedule 12-16, Insurance Companies, Supplementary Insurance Information [Line Items] | ||||||
| Deferred Policy Acquisition Costs | $ 357.2 | $ 322.1 | $ 296.2 | |||
| Net Reserves for Losses and LAE | 4,443.1 | 3,950.6 | 3,232.8 | $ 2,813.2 | ||
| Net Reserves for Unearned Premiums | 1,757.2 | 1,744.1 | 1,692.8 | |||
| Net earned premiums | [1] | 2,831.9 | 2,889.7 | 2,614.5 | ||
| Net Investment Income | 326.3 | 318.0 | 275.7 | |||
| Losses and LAE Expenses | (1,546.7) | (1,717.8) | (1,553.0) | |||
| Policy Acquisition Expenses | (422.4) | (420.2) | (380.2) | |||
| Net written premiums | 2,836.0 | 2,942.6 | 2,581.9 | |||
| General and Administrative Expenses | (492.0) | (405.9) | (354.5) | |||
| Reinsurance | ||||||
| SEC Schedule 12-16, Insurance Companies, Supplementary Insurance Information [Line Items] | ||||||
| Deferred Policy Acquisition Costs | 183.0 | 73.9 | 94.7 | |||
| Net Reserves for Losses and LAE | 2,509.0 | 2,259.1 | 1,859.7 | |||
| Net Reserves for Unearned Premiums | 805.2 | 1,164.1 | 1,048.3 | |||
| Net earned premiums | 1,623.8 | 1,584.0 | 1,460.0 | |||
| Losses and LAE Expenses | (864.4) | (976.5) | (941.9) | |||
| Policy Acquisition Expenses | (243.4) | (193.2) | (171.6) | |||
| Net written premiums | 1,604.9 | 1,666.9 | 1,483.9 | |||
| General and Administrative Expenses | (303.3) | (264.2) | (233.9) | |||
| Insurance | ||||||
| SEC Schedule 12-16, Insurance Companies, Supplementary Insurance Information [Line Items] | ||||||
| Deferred Policy Acquisition Costs | 174.2 | 248.2 | 201.5 | |||
| Net Reserves for Losses and LAE | 1,934.1 | 1,691.5 | 1,373.1 | |||
| Net Reserves for Unearned Premiums | 952.0 | 580.0 | 644.5 | |||
| Net earned premiums | 1,208.1 | 1,305.7 | 1,154.5 | |||
| Losses and LAE Expenses | (682.3) | (741.3) | (611.1) | |||
| Policy Acquisition Expenses | (179.0) | (227.0) | (208.6) | |||
| Net written premiums | 1,231.1 | 1,275.7 | 1,098.0 | |||
| General and Administrative Expenses | $ (188.7) | $ (141.7) | $ (120.6) | |||
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