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Reserve for Loss and Loss Expense - Schedule of (Favorable)/ Unfavorable Prior Year Development (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
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 | $ 285,271 | $ 9,954 | $ (78,890)
Favorable or Unfavorable Loss Development |  |  |
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 | 285,300 | 10,000 | (78,900)
General liability | Favorable or Unfavorable Loss Development |  |  |
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 | 316,000 | 55,000 | (5,000)
Commercial automobile | Favorable or Unfavorable Loss Development |  |  |
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 | 19,500 | 8,000 | 22,500
Workers Compensation | Favorable or Unfavorable Loss Development |  |  |
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 | (45,000) | (74,500) | (70,000)
Businessowners’ policies | Favorable or Unfavorable Loss Development |  |  |
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 | (1,700) | 7,600 | (7,300)
Commercial Property | Favorable or Unfavorable Loss Development |  |  |
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 | (23,400) | 700 | (1,600)
Bonds | Favorable or Unfavorable Loss Development |  |  |
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) | 0 | (10,000)
Homeowners | Favorable or Unfavorable Loss Development |  |  |
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 | (1,400) | 4,600 | (600)
Personal automobile | Favorable or Unfavorable Loss Development |  |  |
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 | 11,100 | 15,300 | 500
E&S Casualty Lines | Favorable or Unfavorable Loss Development |  |  |
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 | 20,000 | (5,000) | (5,000)
E&S Property Lines | Favorable or Unfavorable Loss Development |  |  |
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 | (4,900) | (1,600) | (2,500)
Other | Favorable or Unfavorable Loss Development |  |  |
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 | $ 100 | $ (100) | $ 100

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