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Reserve for Loss and Loss Expense - Narrative (Details) - USD ($) $ in Thousands | 3 Months Ended
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Mar. 31, 2024 | Mar. 31, 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 | $ 15,773 | $ (12,970)
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 | 35,000 |
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 |  | (10,000)
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 |  | $ 2,000
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 | 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) |
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 |
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 | $ (19,200) |

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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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