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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 ($)
Dec. 31, 2016
USD ($)
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