v3.26.1
Segment Information - Summary of Operating Results by Segment (Details) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Segment Reporting [Line Items]        
Net premiums earned $ 1,497,767 $ 1,366,738 $ 2,950,180 $ 2,649,808
Total incurred losses and loss adjustment expenses     1,906,231 2,160,850
Policy acquisition costs 250,328 227,880 490,830 456,601
Other operating expenses 122,918 96,025 246,805 175,478
Net investment income 89,763 78,759 175,399 160,238
Net realized investment gains 86,512 23,480 81,970 46,801
Other income 7,723 8,908 14,026 14,916
Interest expense (7,909) (7,195) (14,726) (14,383)
Income before income taxes 327,330 206,748 562,983 64,451
Net income 263,502 166,472 453,922 58,145
Operating Segments        
Segment Reporting [Line Items]        
Net premiums earned 1,497,800 1,366,700 2,950,200 2,649,800
Losses 826,800 797,200 1,623,500 1,866,600
Loss adjustment expenses 146,600 142,800 282,800 294,300
Total incurred losses and loss adjustment expenses 973,400 940,000 1,906,300 2,160,900
Policy acquisition costs 250,300 227,900 490,800 456,600
Other operating expenses 122,900 96,000 246,800 175,500
Underwriting gain (loss) 151,200 102,800 306,300 (143,200)
Net investment income 89,800 78,800 175,400 160,200
Net realized investment gains 86,500 23,500 82,000 46,800
Other income 7,700 8,800 14,000 15,000
Interest expense (7,900) (7,200) (14,700) (14,300)
Income before income taxes 327,300 206,700 563,000 64,500
Net income 263,500 166,500 453,900 58,100
Property & Casualty        
Segment Reporting [Line Items]        
Net premiums earned 1,490,452 1,359,342 2,935,548 2,635,100
Property & Casualty | Operating Segments        
Segment Reporting [Line Items]        
Net premiums earned 1,490,500 1,359,300 2,935,600 2,635,100
Losses 823,500 793,300 1,616,200 1,859,000
Loss adjustment expenses 146,100 142,300 281,800 293,300
Total incurred losses and loss adjustment expenses 969,600 935,600 1,898,000 2,152,300
Policy acquisition costs 247,400 225,000 485,200 450,800
Other operating expenses 122,100 95,200 245,200 174,100
Underwriting gain (loss) 151,400 103,500 307,200 (142,100)
Other | Operating Segments        
Segment Reporting [Line Items]        
Net premiums earned 7,300 7,400 14,600 14,700
Losses 3,300 3,900 7,300 7,600
Loss adjustment expenses 500 500 1,000 1,000
Total incurred losses and loss adjustment expenses 3,800 4,400 8,300 8,600
Policy acquisition costs 2,900 2,900 5,600 5,800
Other operating expenses 800 800 1,600 1,400
Underwriting gain (loss) $ (200) $ (700) $ (900) $ (1,100)