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Liability for Unpaid Losses and Loss Adjustment Expenses - Additional Information (Detail) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2023 | Jun. 30, 2022 | Jun. 30, 2023 | Jun. 30, 2022
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Changes in prior year reserve | $ 51 | $ (3,571) | $ 51 | $ (6,634)
Commercial Specialty |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Changes in prior year reserve | 5,000 | (2,300) | 6,500 | (400)
Commercial Specialty | Property Lines | Accident Years 2015 and 2018 through 2021 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Changes in prior year reserve |  | (3,400) |  |
Commercial Specialty | Property Lines | Accident years 2015, 2020 and 2022 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Changes in prior year reserve | (1,000) |  |  |
Commercial Specialty | Property Lines | Accident Years 2015, 2018, 2019 and 2021 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Changes in prior year reserve |  |  |  | (1,500)
Commercial Specialty | Property Lines | Accident Yeas 2015, 2019, 2020, 2021 and 2022 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Changes in prior year reserve |  |  | (800) |
Commercial Specialty | General Liability | Accident Years Prior to 2006 and 2017 through 2022 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Changes in prior year reserve | 6,100 |  |  |
Commercial Specialty | General Liability | Accident Years Prior to 2005 and 2005 through 2007 and 2010 through 2021 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Changes in prior year reserve |  |  |  | 1,200
Commercial Specialty | General Liability | Accident Years 2005 2010 through 2015, 2016, 2017, 2018, 2019, 2020 and 2021 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Changes in prior year reserve |  | 1,200 |  |
Commercial Specialty | General Liability | Accident Years Prior to 2006, 2011, 2013, 2015, 2017 and 2019 through 2022 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Changes in prior year reserve |  |  | 7,300 |
Reinsurance Operations |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Changes in prior year reserve | 1,000 | (1,200) | 1,000 | (1,200)
Reinsurance Operations | General Liability |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Changes in prior year reserve | (100) |  | (100) |
Reinsurance Operations | Professional | Accident Year 2022 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Changes in prior year reserve | 1,100 |  | 1,100 |
Reinsurance Operations | Professional | Accident Year 2016 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Changes in prior year reserve |  | (1,200) |  | (1,200)
Exited Lines |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Changes in prior year reserve | (5,900) | (100) | (7,400) | (5,000)
Exited Lines | Property Lines | Accident Years 2011, 2015 through 2018 and 2021 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Changes in prior year reserve |  | 2,000 |  |
Exited Lines | Property Lines | Accident Years 2014, 2017, 2020, 2021 and 2022 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Changes in prior year reserve | 1,100 |  |  |
Exited Lines | Property Lines | Accident Years 2011, 2015 through 2017, 2018, 2020 and 2021 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Changes in prior year reserve |  |  |  | (200)
Exited Lines | Property Lines | Accident Years 2014, 2016, 2017, 2020, 2021 and 2022 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Changes in prior year reserve |  |  | 1,300 |
Exited Lines | General Liability | Accident Years 2014 through 2017 and 2022 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Changes in prior year reserve |  |  | (1,400) |
Exited Lines | General Liability | Accident years 2014 through 2017 and 2019 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Changes in prior year reserve | (900) |  |  |
Exited Lines | General Liability | Accident Years 2017, 2018, 2019 and 2021 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Changes in prior year reserve |  |  |  | (600)
Exited Lines | Reinsurance | Accident Years 2012 and 2015 through 2021 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Changes in prior year reserve | $ (6,200) |  | $ (7,300) |
Exited Lines | Reinsurance | Accident Years 2017 through 2021 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Changes in prior year reserve |  | $ (2,100) |  | $ (4,300)

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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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