v3.26.1
Reserve for Loss and Loss Expense
 6 Months Ended
Jun. 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:

Six Months ended
June 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 year1,658,989 1,535,575 
Prior years(27,219)34,648 
Total incurred loss and loss expense1,631,770 1,570,223 
Paid loss and loss expense for claims occurring in the:  
Current year342,237 320,366 
Prior years884,034 865,344 
Total paid loss and loss expense1,226,271 1,185,710 
Net reserve for loss and loss expense, at end of period6,753,054 5,952,069 
Add: Reinsurance recoverable on unpaid loss and loss expense, at end of period928,385 859,087 
Gross reserve for loss and loss expense, at end of period7,681,439 6,811,156 

Favorable prior year property reserve development was $27.2 million in Six Months 2026. We did not record any favorable or unfavorable prior year casualty reserve development in Six Months 2026.

Prior year reserve development in Six Months 2025 was unfavorable by $34.6 million, consisting of $50.0 million of unfavorable casualty reserve development, partially offset by $15.4 million of favorable property reserve development. Our Standard Commercial Lines segment drove the unfavorable casualty reserve development consisting of (i) $25.0 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 primarily in accident years 2022 and 2023. We also had an unfavorable development of $5.0 million in our personal automobile line of business, primarily related to increased severities in accident year 2024.