v3.25.2
Segment Information - Summary of Premiums Written and Earned by Segment (Details) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2025
Jun. 30, 2024
Jun. 30, 2025
Jun. 30, 2024
Segment Reporting Information [Line Items]        
Net premiums earned $ 1,366,738 $ 1,236,024 $ 2,649,808 $ 2,402,703
Operating Segments        
Segment Reporting Information [Line Items]        
Net premiums earned 1,366,700 1,236,000 2,649,800 2,402,700
Direct premiums written 1,485,000 1,387,300 2,930,400 2,688,400
Private passenger automobile | Operating Segments        
Segment Reporting Information [Line Items]        
Net premiums earned 887,400 799,600 1,746,000 1,553,900
Direct premiums written 881,500 847,600 1,788,000 1,673,100
Homeowners | Operating Segments        
Segment Reporting Information [Line Items]        
Net premiums earned 316,900 283,600 572,900 550,500
Direct premiums written 434,500 361,900 778,700 664,000
Commercial automobile | Operating Segments        
Segment Reporting Information [Line Items]        
Net premiums earned 95,900 94,200 191,200 183,400
Direct premiums written 93,900 98,800 200,400 202,800
Other | Operating Segments        
Segment Reporting Information [Line Items]        
Net premiums earned 66,500 58,600 139,700 114,900
Direct premiums written 75,100 79,000 163,300 148,500
Property & Casualty        
Segment Reporting Information [Line Items]        
Net premiums earned 1,359,342 1,228,696 2,635,100 2,388,065
Direct premiums written 1,477,169 1,380,511 2,915,636 2,674,986
Property & Casualty | Operating Segments        
Segment Reporting Information [Line Items]        
Net premiums earned 1,359,300 1,228,700 2,635,100 2,388,100
Direct premiums written 1,477,200 1,380,500 2,915,600 2,675,000
Property & Casualty | Private passenger automobile | Operating Segments        
Segment Reporting Information [Line Items]        
Net premiums earned 887,400 799,600 1,746,000 1,553,900
Direct premiums written 881,500 847,600 1,788,000 1,673,100
Property & Casualty | Homeowners | Operating Segments        
Segment Reporting Information [Line Items]        
Net premiums earned 316,900 283,600 572,900 550,500
Direct premiums written 434,500 361,900 778,700 664,000
Property & Casualty | Commercial automobile | Operating Segments        
Segment Reporting Information [Line Items]        
Net premiums earned 95,900 94,200 191,200 183,400
Direct premiums written 93,900 98,800 200,400 202,800
Property & Casualty | Other | Operating Segments        
Segment Reporting Information [Line Items]        
Net premiums earned 59,100 51,300 125,000 100,300
Direct premiums written 67,300 72,200 148,500 135,100
Other | Operating Segments        
Segment Reporting Information [Line Items]        
Net premiums earned 7,400 7,300 14,700 14,600
Direct premiums written 7,800 6,800 14,800 13,400
Other | Private passenger automobile | Operating Segments        
Segment Reporting Information [Line Items]        
Net premiums earned 0 0 0 0
Direct premiums written 0 0 0 0
Other | Homeowners | Operating Segments        
Segment Reporting Information [Line Items]        
Net premiums earned 0 0 0 0
Direct premiums written 0 0 0 0
Other | Commercial automobile | Operating Segments        
Segment Reporting Information [Line Items]        
Net premiums earned 0 0 0 0
Direct premiums written 0 0 0 0
Other | Other | Operating Segments        
Segment Reporting Information [Line Items]        
Net premiums earned 7,400 7,300 14,700 14,600
Direct premiums written $ 7,800 $ 6,800 $ 14,800 $ 13,400