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Reserve for Loss and Loss Expense - Narrative (Details) - USD ($) $ in Thousands | 3 Months Ended
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Mar. 31, 2025 | Mar. 31, 2024
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |
Incurred loss and loss expense for claims occurring in the prior year | $ (13,667) | $ 15,773
Casualty reserve |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |
Incurred loss and loss expense for claims occurring in the prior year | 5,000 | 35,000
Casualty reserve | Standard Commercial Lines | General liability |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |
Incurred loss and loss expense for claims occurring in the prior year |  | 50,000
Casualty reserve | Standard Commercial Lines | Workers' compensation |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |
Incurred loss and loss expense for claims occurring in the prior year |  | (15,000)
Casualty reserve | Standard Personal Lines | Personal automobile |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |
Incurred loss and loss expense for claims occurring in the prior year | 5,000 | 5,000
Casualty reserve | Standard Personal Lines | Homeowners |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |
Incurred loss and loss expense for claims occurring in the prior year |  | (5,000)
Property lines |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |
Incurred loss and loss expense for claims occurring in the prior year | $ (18,700) | $ (19,200)

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