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Reserve for Loss and Loss Expense - Narrative (Details) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2024 | Jun. 30, 2023 | Jun. 30, 2024 | Jun. 30, 2023
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 |  |  | $ 187,121 | $ (8,067)
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 | $ 176,000 | $ (3,500) | 211,000 | (16,500)
Casualty reserve | 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) | (17,500)
Casualty reserve | E&S |  |  |  |
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)
Casualty reserve | 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 | 6,000
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 |  |  | 216,000 |
Casualty reserve | Standard Commercial Lines | Commercial 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 |  |  | 10,000 |
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 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 |  |  | $ (23,900) | $ 8,400

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- Definition Amount, after effects of reinsurance, of expense (reversal of expense) for claims incurred in prior reporting periods and related claims settlement costs. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480081/944-40-50-3 + Details
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