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Liabilities for Outstanding Claims, Losses and Loss Adjustment Expenses (Schedule of Incurred Claims Development) (Details) $ in Millions | Dec. 31, 2025 USD ($) Claim | Dec. 31, 2024 USD ($) | Dec. 31, 2023 USD ($) | Dec. 31, 2022 USD ($) | Dec. 31, 2021 USD ($) | Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($)
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Commercial Multiple Peril Line [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | $ 4,911.4 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | 3,580.4 |  |  |  |  |  |  |  |  |
Unallocated loss adjustment expense | 26.0 |  |  |  |  |  |  |  |  |
Net reserves | 1,465.8 |  |  |  |  |  |  |  |  |
Commercial Multiple Peril Line [Member] | Year 2018 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 502.6 | $ 500.1 | $ 499.7 | $ 495.8 | $ 490.6 | $ 489.5 | $ 495.6 | $ 511.1 |  |
IBNR | $ 12.8 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 15,935 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 462.9 | 454.9 | 429.5 | 403.6 | 362.9 | 326.4 | 274.1 | 165.7 |  |
Commercial Multiple Peril Line [Member] | Year 2019 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 536.1 | 537.4 | 540.2 | 542.6 | 533.1 | 527.0 | 520.2 |  |  |
IBNR | $ 18.0 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 15,266 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 490.8 | 470.4 | 444.5 | 396.3 | 348.7 | 288.5 | 156.5 |  |  |
Commercial Multiple Peril Line [Member] | Year 2020 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 511.8 | 509.5 | 514.9 | 531.5 | 546.7 | 562.1 |  |  |  |
IBNR | $ 20.5 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 12,972 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 461.9 | 434.2 | 401.0 | 364.2 | 318.6 | 200.8 |  |  |  |
Commercial Multiple Peril Line [Member] | Year 2021 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 650.1 | 651.9 | 655.1 | 658.7 | 673.5 |  |  |  |  |
IBNR | $ 29.2 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 14,854 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 564.2 | 513.8 | 450.0 | 392.6 | 245.1 |  |  |  |  |
Commercial Multiple Peril Line [Member] | Year 2022 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 722.5 | 733.8 | 749.2 | 748.1 |  |  |  |  |  |
IBNR | $ 51.9 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 13,975 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 575.5 | 513.8 | 441.2 | 198.2 |  |  |  |  |  |
Commercial Multiple Peril Line [Member] | Year 2023 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 672.4 | 684.1 | 698.3 |  |  |  |  |  |  |
IBNR | $ 95.4 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 12,765 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 460.1 | 392.1 | 240.5 |  |  |  |  |  |  |
Commercial Multiple Peril Line [Member] | Year 2024 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 633.1 | 662.4 |  |  |  |  |  |  |  |
IBNR | $ 157.6 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 12,025 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 355.2 | 217.9 |  |  |  |  |  |  |  |
Commercial Multiple Peril Line [Member] | Year 2025 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 682.8 |  |  |  |  |  |  |  |  |
IBNR | $ 304.8 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 9,297 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 209.8 |  |  |  |  |  |  |  |  |
Commercial Multiple Peril Line [Member] | Year 2018 to 2025 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Total reserves for accident years | 1,331.0 |  |  |  |  |  |  |  |  |
Commercial Multiple Peril Line [Member] | Years 2017 and Prior [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Total reserves for accident years | 108.8 |  |  |  |  |  |  |  |  |
Workers' Compensation Line [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 1,687.1 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | 1,158.5 |  |  |  |  |  |  |  |  |
Unallocated loss adjustment expense | 21.2 |  |  |  |  |  |  |  |  |
Net reserves | 639.4 |  |  |  |  |  |  |  |  |
Workers' Compensation Line [Member] | Year 2016 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 115.6 | 117.2 | 118.3 | 122.3 | 124.9 | 128.3 | 133.5 | 139.9 | $ 152.8 | $ 158.9
IBNR | $ 5.1 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 12,853 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 104.6 | 104.7 | 103.5 | 102.1 | 100.1 | 97.2 | 93.3 | 84.4 | 67.0 | 29.2
Workers' Compensation Line [Member] | Year 2017 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 121.8 | 123.8 | 125.7 | 129.6 | 132.4 | 136.7 | 139.9 | 148.7 | 159.6 |
IBNR | $ 5.6 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 13,496 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 109.6 | 108.1 | 106.2 | 102.6 | 99.0 | 92.7 | 82.0 | 63.7 | 28.5 |
Workers' Compensation Line [Member] | Year 2018 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 139.8 | 142.7 | 145.8 | 149.2 | 150.8 | 152.6 | 161.3 | 165.2 |  |
IBNR | $ 8.4 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 15,075 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 123.5 | 121.6 | 117.8 | 112.0 | 104.2 | 91.7 | 72.0 | 32.2 |  |
Workers' Compensation Line [Member] | Year 2019 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 155.6 | 159.2 | 159.5 | 163.2 | 162.9 | 165.0 | 170.5 |  |  |
IBNR | $ 9.7 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 15,551 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 134.3 | 128.7 | 124.5 | 116.2 | 102.4 | 75.7 | 30.4 |  |  |
Workers' Compensation Line [Member] | Year 2020 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 136.0 | 139.8 | 142.4 | 150.6 | 166.8 | 167.1 |  |  |  |
IBNR | $ 9.9 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 12,237 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 112.9 | 109.1 | 102.9 | 91.8 | 71.4 | 28.8 |  |  |  |
Workers' Compensation Line [Member] | Year 2021 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 172.5 | 174.0 | 175.5 | 180.8 | 178.5 |  |  |  |  |
IBNR | $ 12.0 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 14,827 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 134.0 | 125.5 | 109.4 | 85.3 | 40.6 |  |  |  |  |
Workers' Compensation Line [Member] | Year 2022 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 206.1 | 207.4 | 205.9 | 198.5 |  |  |  |  |  |
IBNR | $ 17.3 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 15,934 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 149.8 | 132.9 | 101.8 | 41.4 |  |  |  |  |  |
Workers' Compensation Line [Member] | Year 2023 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 215.6 | 215.7 | 202.3 |  |  |  |  |  |  |
IBNR | $ 23.4 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 14,625 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 141.7 | 107.0 | 48.8 |  |  |  |  |  |  |
Workers' Compensation Line [Member] | Year 2024 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 206.3 | 209.1 |  |  |  |  |  |  |  |
IBNR | $ 43.1 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 13,751 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 101.7 | 44.1 |  |  |  |  |  |  |  |
Workers' Compensation Line [Member] | Year 2025 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 217.8 |  |  |  |  |  |  |  |  |
IBNR | $ 89.5 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 13,584 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 46.4 |  |  |  |  |  |  |  |  |
Workers' Compensation Line [Member] | Years 2016 to 2025 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Total reserves for accident years | 528.6 |  |  |  |  |  |  |  |  |
Workers' Compensation Line [Member] | Years 2015 and Prior [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Total reserves for accident years | 89.6 |  |  |  |  |  |  |  |  |
Commercial Automobile Line [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 1,245.5 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | 714.9 |  |  |  |  |  |  |  |  |
Unallocated loss adjustment expense | 4.6 |  |  |  |  |  |  |  |  |
Net reserves | 554.6 |  |  |  |  |  |  |  |  |
Commercial Automobile Line [Member] | Year 2019 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 178.9 | 179.9 | 181.4 | 174.6 | 169.7 | 167.9 | 161.0 |  |  |
IBNR | $ 5.0 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 9,797 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 167.9 | 163.5 | 147.9 | 126.5 | 94.8 | 64.5 | 27.1 |  |  |
Commercial Automobile Line [Member] | Year 2020 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 131.0 | 132.4 | 134.5 | 140.2 | 141.5 | 153.2 |  |  |  |
IBNR | $ 5.4 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 5,911 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 119.7 | 112.0 | 96.3 | 71.4 | 42.1 | 21.0 |  |  |  |
Commercial Automobile Line [Member] | Year 2021 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 145.4 | 144.6 | 146.1 | 156.5 | 154.1 |  |  |  |  |
IBNR | $ 10.9 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 6,132 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 120.0 | 98.8 | 73.7 | 45.2 | 17.7 |  |  |  |  |
Commercial Automobile Line [Member] | Year 2022 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 171.7 | 168.7 | 173.3 | 157.5 |  |  |  |  |  |
IBNR | $ 21.4 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 6,185 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 122.2 | 80.5 | 53.0 | 18.9 |  |  |  |  |  |
Commercial Automobile Line [Member] | Year 2023 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 194.1 | 179.4 | 171.5 |  |  |  |  |  |  |
IBNR | $ 40.3 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 6,271 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 101.2 | 55.3 | 23.7 |  |  |  |  |  |  |
Commercial Automobile Line [Member] | Year 2024 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 203.6 | 182.7 |  |  |  |  |  |  |  |
IBNR | $ 80.9 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 6,059 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 58.4 | 23.0 |  |  |  |  |  |  |  |
Commercial Automobile Line [Member] | Year 2025 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 220.8 |  |  |  |  |  |  |  |  |
IBNR | $ 163.7 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 5,419 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 25.5 |  |  |  |  |  |  |  |  |
Commercial Automobile Line [Member] | Years 2019 to 2025 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Total reserves for accident years | 530.6 |  |  |  |  |  |  |  |  |
Commercial Automobile Line [Member] | Years 2018 and Prior [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Total reserves for accident years | 19.4 |  |  |  |  |  |  |  |  |
Core - General Liability And Umbrella - Occurrence [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 731.8 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | 352.3 |  |  |  |  |  |  |  |  |
Unallocated loss adjustment expense | 2.9 |  |  |  |  |  |  |  |  |
Net reserves | 403.5 |  |  |  |  |  |  |  |  |
Core - General Liability And Umbrella - Occurrence [Member] | Year 2016 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 65.2 | 61.9 | 59.2 | 54.2 | 54.5 | 53.7 | 55.8 | 57.8 | 61.0 | 58.5
IBNR | $ 2.6 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 1,218 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 56.5 | 54.1 | 52.0 | 38.7 | 34.4 | 31.7 | 25.3 | 14.8 | 7.3 | $ 0.7
Core - General Liability And Umbrella - Occurrence [Member] | Year 2017 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 60.2 | 60.9 | 60.8 | 61.0 | 62.9 | 63.0 | 66.3 | 67.1 | 58.2 |
IBNR | $ 4.1 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 1,036 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 51.8 | 49.0 | 46.8 | 42.6 | 33.9 | 27.1 | 19.3 | 9.0 | $ 2.3 |
Core - General Liability And Umbrella - Occurrence [Member] | Year 2018 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 60.4 | 64.3 | 65.0 | 63.2 | 63.3 | 60.3 | 61.1 | 58.8 |  |
IBNR | $ 6.4 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 978 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 48.2 | 45.7 | 40.7 | 38.1 | 27.2 | 18.8 | 4.4 | 1.0 |  |
Core - General Liability And Umbrella - Occurrence [Member] | Year 2019 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 71.3 | 74.5 | 73.7 | 69.3 | 60.3 | 60.0 | 58.9 |  |  |
IBNR | $ 7.8 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 882 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 57.1 | 49.9 | 38.2 | 28.2 | 16.5 | 8.7 | 4.3 |  |  |
Core - General Liability And Umbrella - Occurrence [Member] | Year 2020 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 43.9 | 44.9 | 52.1 | 53.4 | 58.9 | 56.2 |  |  |  |
IBNR | $ 9.1 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 561 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 27.8 | 24.7 | 17.8 | 11.9 | 9.2 | 2.1 |  |  |  |
Core - General Liability And Umbrella - Occurrence [Member] | Year 2021 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 68.2 | 69.6 | 73.7 | 70.0 | 58.3 |  |  |  |  |
IBNR | $ 19.5 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 529 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 40.4 | 29.6 | 17.3 | 6.6 | 1.5 |  |  |  |  |
Core - General Liability And Umbrella - Occurrence [Member] | Year 2022 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 89.3 | 75.2 | 76.6 | 63.3 |  |  |  |  |  |
IBNR | $ 27.4 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 542 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 39.8 | 19.1 | 9.3 | 0.4 |  |  |  |  |  |
Core - General Liability And Umbrella - Occurrence [Member] | Year 2023 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 79.7 | 77.6 | 72.2 |  |  |  |  |  |  |
IBNR | $ 43.2 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 443 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 18.3 | 11.4 | 5.4 |  |  |  |  |  |  |
Core - General Liability And Umbrella - Occurrence [Member] | Year 2024 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 94.9 | 93.3 |  |  |  |  |  |  |  |
IBNR | $ 65.1 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 468 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 11.0 | 2.6 |  |  |  |  |  |  |  |
Core - General Liability And Umbrella - Occurrence [Member] | Year 2025 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 98.7 |  |  |  |  |  |  |  |  |
IBNR | $ 84.0 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 428 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 1.4 |  |  |  |  |  |  |  |  |
Core - General Liability And Umbrella - Occurrence [Member] | Years 2016 to 2025 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Total reserves for accident years | 379.5 |  |  |  |  |  |  |  |  |
Core - General Liability And Umbrella - Occurrence [Member] | Years 2015 and Prior [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Total reserves for accident years | 21.1 |  |  |  |  |  |  |  |  |
Specialty Property And Casualty [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 1,651.1 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | 1,111.3 |  |  |  |  |  |  |  |  |
Unallocated loss adjustment expense | 14.7 |  |  |  |  |  |  |  |  |
Net reserves | 595.6 |  |  |  |  |  |  |  |  |
Specialty Property And Casualty [Member] | Year 2018 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 188.7 | 189.3 | 191.1 | 191.1 | 190.2 | 193.7 | 194.1 | 193.0 |  |
IBNR | $ 5.5 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 6,382 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 179.7 | 176.5 | 170.4 | 158.6 | 140.3 | 124.9 | 107.9 | $ 56.0 |  |
Specialty Property And Casualty [Member] | Year 2019 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 228.4 | 231.0 | 236.8 | 237.1 | 225.7 | 209.4 | 212.2 |  |  |
IBNR | $ 9.9 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 6,469 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 208.1 | 203.5 | 187.1 | 164.9 | 136.5 | 113.9 | 71.5 |  |  |
Specialty Property And Casualty [Member] | Year 2020 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 161.2 | 165.6 | 169.5 | 164.9 | 170.8 | 181.1 |  |  |  |
IBNR | $ 10.0 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 5,219 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 142.8 | 136.3 | 121.9 | 101.2 | 84.0 | 40.4 |  |  |  |
Specialty Property And Casualty [Member] | Year 2021 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 205.9 | 211.2 | 210.2 | 213.9 | 202.9 |  |  |  |  |
IBNR | $ 19.4 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 5,912 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 167.5 | 149.1 | 125.9 | 106.6 | 59.2 |  |  |  |  |
Specialty Property And Casualty [Member] | Year 2022 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 217.8 | 222.2 | 215.3 | 218.3 |  |  |  |  |  |
IBNR | $ 36.2 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 5,442 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 153.8 | 127.6 | 106.5 | 60.7 |  |  |  |  |  |
Specialty Property And Casualty [Member] | Year 2023 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 208.4 | 214.2 | 229.7 |  |  |  |  |  |  |
IBNR | $ 58.4 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 4,526 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 117.1 | 92.4 | 61.1 |  |  |  |  |  |  |
Specialty Property And Casualty [Member] | Year 2024 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 214.1 | 212.8 |  |  |  |  |  |  |  |
IBNR | $ 87.9 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 4,200 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 86.3 | 49.3 |  |  |  |  |  |  |  |
Specialty Property And Casualty [Member] | Year 2025 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 226.6 |  |  |  |  |  |  |  |  |
IBNR | $ 135.4 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 2,939 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 56.0 |  |  |  |  |  |  |  |  |
Specialty Property And Casualty [Member] | Year 2018 to 2025 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Total reserves for accident years | 539.8 |  |  |  |  |  |  |  |  |
Specialty Property And Casualty [Member] | Years 2017 and Prior [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Total reserves for accident years | 41.1 |  |  |  |  |  |  |  |  |
Specialty General Liability Claims Made [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 1,025.6 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | 598.6 |  |  |  |  |  |  |  |  |
Unallocated loss adjustment expense | 6.6 |  |  |  |  |  |  |  |  |
Net reserves | 442.3 |  |  |  |  |  |  |  |  |
Specialty General Liability Claims Made [Member] | Year 2019 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 128.8 | 129.0 | 126.7 | 127.6 | 125.6 | 119.5 | 119.8 |  |  |
IBNR | $ 3.4 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 1,201 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 120.1 | 115.4 | 107.4 | 95.4 | 77.0 | 53.3 | $ 16.5 |  |  |
Specialty General Liability Claims Made [Member] | Year 2020 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 118.0 | 122.5 | 119.1 | 123.3 | 134.2 | 137.3 |  |  |  |
IBNR | $ 5.8 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 1,193 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 104.6 | 101.2 | 89.4 | 75.0 | 50.6 | $ 16.8 |  |  |  |
Specialty General Liability Claims Made [Member] | Year 2021 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 131.8 | 128.6 | 134.6 | 144.8 | 148.2 |  |  |  |  |
IBNR | $ 13.2 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 1,083 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 105.6 | 92.4 | 76.7 | 49.9 | 15.8 |  |  |  |  |
Specialty General Liability Claims Made [Member] | Year 2022 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 134.6 | 137.6 | 149.0 | 162.3 |  |  |  |  |  |
IBNR | $ 21.8 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 1,089 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 94.2 | 78.2 | 54.0 | 18.1 |  |  |  |  |  |
Specialty General Liability Claims Made [Member] | Year 2023 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 158.1 | 167.7 | 170.5 |  |  |  |  |  |  |
IBNR | $ 36.1 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 1,383 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 86.7 | 55.4 | 17.9 |  |  |  |  |  |  |
Specialty General Liability Claims Made [Member] | Year 2024 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 179.0 | 183.6 |  |  |  |  |  |  |  |
IBNR | $ 63.4 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 1,524 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 64.0 | 24.4 |  |  |  |  |  |  |  |
Specialty General Liability Claims Made [Member] | Year 2025 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 175.3 |  |  |  |  |  |  |  |  |
IBNR | $ 87.3 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 2,672 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 23.4 |  |  |  |  |  |  |  |  |
Specialty General Liability Claims Made [Member] | Years 2019 to 2025 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Total reserves for accident years | 427.0 |  |  |  |  |  |  |  |  |
Specialty General Liability Claims Made [Member] | Years 2018 and Prior [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Total reserves for accident years | 8.7 |  |  |  |  |  |  |  |  |
Personal Automobile Lines [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 2,414.5 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | 1,614.6 |  |  |  |  |  |  |  |  |
Unallocated loss adjustment expense | 16.2 |  |  |  |  |  |  |  |  |
Net reserves | 867.8 |  |  |  |  |  |  |  |  |
Personal Automobile Lines [Member] | Year 2021 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 403.6 | 403.0 | 408.5 | 411.6 | 407.2 |  |  |  |  |
IBNR | $ 6.6 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 30,846 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 380.7 | 353.0 | 304.4 | 225.9 | $ 106.4 |  |  |  |  |
Personal Automobile Lines [Member] | Year 2022 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 458.7 | 456.6 | 458.6 | 441.9 |  |  |  |  |  |
IBNR | $ 16.3 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 33,974 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 403.5 | 346.0 | 255.0 | 117.2 |  |  |  |  |  |
Personal Automobile Lines [Member] | Year 2023 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 523.0 | 511.1 | 489.9 |  |  |  |  |  |  |
IBNR | $ 42.6 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 35,474 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 400.7 | 296.4 | 143.1 |  |  |  |  |  |  |
Personal Automobile Lines [Member] | Year 2024 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 497.7 | 494.7 |  |  |  |  |  |  |  |
IBNR | $ 90.5 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 31,374 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 286.5 | 142.9 |  |  |  |  |  |  |  |
Personal Automobile Lines [Member] | Year 2025 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 531.5 |  |  |  |  |  |  |  |  |
IBNR | $ 263.1 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 26,157 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 143.2 |  |  |  |  |  |  |  |  |
Personal Automobile Lines [Member] | Years 2021 to 2025 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Total reserves for accident years | 799.9 |  |  |  |  |  |  |  |  |
Personal Automobile Lines [Member] | Years 2020 and Prior [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Total reserves for accident years | 51.7 |  |  |  |  |  |  |  |  |
Homeowners [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 2,541.9 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | 2,263.7 |  |  |  |  |  |  |  |  |
Unallocated loss adjustment expense | 5.4 |  |  |  |  |  |  |  |  |
Net reserves | 296.9 |  |  |  |  |  |  |  |  |
Homeowners [Member] | Year 2022 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 561.8 | 559.7 | 557.0 | 548.5 |  |  |  |  |  |
IBNR | $ 5.3 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 35,242 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 546.8 | 537.0 | 511.7 | $ 324.1 |  |  |  |  |  |
Homeowners [Member] | Year 2023 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 855.3 | 863.8 | 874.4 |  |  |  |  |  |  |
IBNR | $ 7.0 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 50,444 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 836.5 | 811.9 | $ 590.4 |  |  |  |  |  |  |
Homeowners [Member] | Year 2024 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 635.6 | 648.6 |  |  |  |  |  |  |  |
IBNR | $ 23.8 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 31,998 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 584.3 | $ 430.9 |  |  |  |  |  |  |  |
Homeowners [Member] | Year 2025 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE, Net of Reinsurance | 489.2 |  |  |  |  |  |  |  |  |
IBNR | $ 124.6 |  |  |  |  |  |  |  |  |
Cumulative Incurred Claim Count | Claim | 19,467 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE, Net of Reinsurance | $ 296.1 |  |  |  |  |  |  |  |  |
Homeowners [Member] | Years 2022 to 2025 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Total reserves for accident years | 278.2 |  |  |  |  |  |  |  |  |
Homeowners [Member] | Years 2021 and Prior [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Total reserves for accident years | $ 13.3 |  |  |  |  |  |  |  |  |

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