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Liability for Unpaid Losses and Loss Adjustment Expenses - Additional Information (Detail) - USD ($) $ in Thousands | 3 Months Ended
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Mar. 31, 2023 | Mar. 31, 2022
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |
Changes in prior year reserve | $ 0 | $ (3,063)
Commercial Specialty |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |
Changes in prior year reserve | 1,500 | 1,900
Commercial Specialty | Property Lines | Accident Years 2018 through 2022 |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |
Changes in prior year reserve | 200 |
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 |  | 1,900
Commercial Specialty | General Liability | Accident Years Prior to 2005 and 2011, 2013, 2015, 2016, 2018 through 2020, 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 |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |
Changes in prior year reserve | (1,500) | (4,900)
Exited Lines | Property Lines | Accident Years 2016 through 2018 and 2020 through 2022 |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |
Changes in prior year reserve | (1,000) |
Exited Lines | Property Lines | Accident Years 2015, 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 |  | (2,100)
Exited Lines | General Liability | Accident Years 2014 through 2022 |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |
Changes in prior year reserve | $ (500) |
Exited Lines | General Liability | Accident Years 2017 through 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 2017 through 2021 |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |
Changes in prior year reserve |  | $ (2,200)

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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 -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (b) -URI https://asc.fasb.org/extlink&oid=116884095&loc=d3e14764-158437 + Details
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