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Liability for Unpaid Losses and Loss Adjustment Expenses - Additional Information (Detail) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2024 | Sep. 30, 2023 | Sep. 30, 2024 | Sep. 30, 2023
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Changes in prior year reserve | $ (34) | $ (51) | $ (115) | $ 0
Maximum |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Changes in prior year reserve | (100) |  |  |
Non-Core Operations |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Changes in prior year reserve |  | (7,800) | 300 | (10,900)
Non-Core Operations | Maximum |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Changes in prior year reserve | (100) |  |  |
Non-Core Operations | Property Lines |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Changes in prior year reserve |  | 500 |  | 1,800
Non-Core Operations | Property Lines | Adverse Development |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Changes in prior year reserve |  | 1,400 |  | 3,400
Non-Core Operations | Property Lines | Favorable Development |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Changes in prior year reserve |  | (900) |  | (1,600)
Non-Core Operations | Casualty Lines |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Changes in prior year reserve |  | 4,500 |  | 6,400
Non-Core Operations | Casualty Lines | Adverse Development |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Changes in prior year reserve |  | 7,100 |  | 11,200
Non-Core Operations | Casualty Lines | Favorable Development |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Changes in prior year reserve |  | (2,600) |  | (4,800)
Non-Core Operations | Reinsurance |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Changes in prior year reserve |  | (12,700) |  | (19,000)
Penn-America Segment |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Changes in prior year reserve |  | 7,800 | (400) | 10,900
Penn-America Segment | Maximum |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Changes in prior year reserve | 100 |  |  |
Penn-America Segment | Property Lines |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Changes in prior year reserve | (3,700) | 1,700 | (4,000) | 800
Penn-America Segment | Casualty Lines |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Changes in prior year reserve | $ 3,700 | 6,100 | $ 3,600 | 10,100
Penn-America Segment | Casualty Lines | Adverse Development |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Changes in prior year reserve |  | 11,300 |  | 16,900
Penn-America Segment | Casualty Lines | Favorable Development |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Changes in prior year reserve |  | $ (5,200) |  | $ (6,800)

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