v3.26.3
Reserve for Loss and Loss Expense
 9 Months Ended
Sep. 30, 2026
Insurance Loss Reserves [Abstract]  
Reserve for Loss and Loss Expense Reserve for Loss and Loss Expense
The table below provides a roll forward of the reserve for loss and loss expense for beginning and ending reserve balances:

Nine Months ended
September 30,
($ in thousands)20262025
Gross reserve for loss and loss expense, at beginning of period$7,225,398 6,589,801 
Less: reinsurance recoverable on unpaid loss and loss expense, at beginning of period877,843 1,022,245 
Net reserve for loss and loss expense, at beginning of period6,347,555 5,567,556 
Incurred loss and loss expense for claims occurring in the:
Current year2,417,011 2,319,158 
Prior years(22,545)70,096 
Total incurred loss and loss expense2,394,466 2,389,254 
Paid loss and loss expense for claims occurring in the:
Current year610,602 594,811 
Prior years1,210,969 1,199,822 
Total paid loss and loss expense1,821,571 1,794,633 
Net reserve for loss and loss expense, at end of period6,920,450 6,162,177 
Add: Reinsurance recoverable on unpaid loss and loss expense, at end of period1,086,045 914,245 
Gross reserve for loss and loss expense, at end of period8,006,495 7,076,422 
Favorable prior year property reserve development was $22.5 million in Nine Months 2026. We did not record any favorable or unfavorable prior year casualty reserve development in Nine Months 2026.

Prior year reserve development in Nine Months 2025 was unfavorable by $70.1 million, consisting of $90.0 million of unfavorable casualty reserve development, partially offset by $19.9 million of favorable property reserve development. Our Standard Commercial Lines segment drove the unfavorable casualty reserve development consisting of (i) $60.0 million in our commercial automobile line of business, related to severities primarily in accident years 2022 through 2024 and (ii) $20.0 million in our general liability line of business, driven by higher severities on umbrella coverages related to commercial automobile claims, primarily in accident years 2022 and 2023. We also had an unfavorable development of $10.0 million in our personal automobile line of business, primarily related to increased severities in accident year 2024.