v3.25.1
Reserves for Losses and Loss Adjustment Expenses
 3 Months Ended
Mar. 31, 2025
Insurance [Abstract]  
Reserves for Losses and Loss Adjustment Expenses Reserves for Losses and Loss Adjustment Expenses
The following table provides a reconciliation of reserves for losses and loss adjustment expenses (“LAE”):
For the Three Months Ended
March 31,
(in millions)20252024
Net reserves - beginning of the year$3,003.9 $2,747.1 
Add:
Losses and LAE incurred during current calendar year, net of reinsurance:
Current accident year147.1 195.2 
Prior accident years1.0 24.8 
Losses and LAE incurred during calendar year, net of reinsurance148.1 220.0 
Deduct:
Losses and LAE payments made during current calendar year, net of reinsurance:
Current accident year38.6 6.7 
Prior accident years144.6 174.8 
Losses and LAE payments made during current calendar year, net of reinsurance:183.2 181.5 
Add/(Deduct):
Foreign exchange adjustments— (1.3)
Net reserves - end of period2,968.8 2,784.3 
Add:
Reinsurance recoverables on unpaid losses and LAE, end of period2,711.4 2,758.8 
Gross reserves - end of period$5,680.2 $5,543.1 
Reserves for losses and LAE represent the estimated indemnity cost and related adjustment expenses necessary to investigate and settle claims. Such estimates are based upon individual case estimates for reported claims, estimates from ceding companies for reinsurance assumed and actuarial estimates for losses that have been incurred but not yet reported to the insurer. Any change in probable ultimate liabilities is reflected in current operating results.
The impact from the unfavorable (favorable) development of prior accident years’ loss and LAE reserves on each reporting segment is presented below: 
For the Three Months Ended
March 31,
(in millions)20252024
Casualty Lines$0.8 $0.7 
Specialty Lines0.1 0.7 
Run-off Lines0.1 23.4 
Total unfavorable (favorable) prior-year development$1.0 $24.8 
The following describes the primary factors behind each segment’s net prior accident year loss reserve development for the three months ended March 31, 2025 and 2024:
•For the three months ended March 31, 2025, net unfavorable development primarily within Casualty Lines related to involuntary pools and other workers’ compensation exposures.
•For the three months ended March 31, 2024, net unfavorable development primarily related to movements within Run-off lines on large individual surety claims and assumed business from our former Malta operations, ArgoGlobal Holdings (Malta) Ltd., which was sold in 2022.
Our reserves represent the best estimate of our ultimate liabilities, based on currently known facts, current law, current technology and reasonable assumptions where facts are not known. Due to the significant uncertainties and related management judgments, there can be no assurance that future favorable or unfavorable loss development, which may be material, will not occur.