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Investments - Additional Information (Detail) | 12 Months Ended
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Dec. 31, 2022 USD ($) Entity | Dec. 31, 2021 USD ($)
Schedule Of Available For Sale Securities [Line Items] |  |
Investments in a single issuer as a percentage of shareholders' equity | 2.40% | 2.00%
Weighted average life of fixed maturities securities | 5 years |
Maturity period of securities that reinvested to fixed income investments | 2 years |
Percentage of book yield due to reinvested to fixed income investments | 3.50% | 2.20%
Fixed maturity securities with market value | $ 0 | $ 0
Investments in insurance enhanced bonds | $ 6,800,000 |
Insurance enhanced bonds as a percentage of total cash and invested assets | 0.50% |
Investments in collateralized mortgage obligations, commercial mortgage-backed securities and taxable municipal bonds | $ 6,800,000 |
Ownership interest exceeds respective investments | 3.00% |
Variable Interest Entity, Not Primary Beneficiary |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Number of VIE's | Entity | 2 |
Ownership interest exceeds respective investments | 3.00% |
One of the Company's variable interest VIE's, invests in distressed securities and assets |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Significant variable interest in carrying value of the non-consolidated VIE | $ 4,800,000 | 8,600,000
Variable interest entities, maximum exposure to loss | 19,000,000.0 | 22,800,000
Third VIE that invests in REIT qualifying assets |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Significant variable interest in carrying value of the non-consolidated VIE | 9,800,000 | 11,700,000
Variable interest entities, maximum exposure to loss | 9,800,000 | $ 11,700,000
Assured Guaranty Corporation |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Investments in collateralized mortgage obligations, commercial mortgage-backed securities and taxable municipal bonds | 5,300,000 |
U.S. Treasuries |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Gross unrealized losses | 8,430,000 |
Obligations of States and Political Subdivisions |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Gross unrealized losses | 1,876,000 |
Mortgage Backed Securities |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Gross unrealized losses | 5,609,000 |
Asset-backed Securities |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Gross unrealized losses | $ 9,151,000 |
Weighted average credit enhancement | 34.20% |
Commercial Mortgage-Backed Securities |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Gross unrealized losses | $ 6,133,000 |
Weighted average credit enhancement | 46.20% |
Corporate Bonds |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Gross unrealized losses | $ 14,858,000 |
Foreign Corporate Bonds |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Gross unrealized losses | 8,059,000.000 |
Ambac Financial Group |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Investments in collateralized mortgage obligations, commercial mortgage-backed securities and taxable municipal bonds | $ 1,500,000 |

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