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v3.25.0.1

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
New Accounting Pronouncements Or Change In Accounting Principle [Line Items] |  |  |
Percentage of comparable consolidated amounts | 95.00% | 95.00% | 95.00%
Original maturity of cash equivalent | 90 days |  |
Minimum period of underwriting workers? compensation insurance from which historical loss data utilize | 39 years |  |
Experience rated commission and other operating costs | $ 1.0 | $ 1.7 | $ 0.1
Advertising expense | $ 0.3 | $ 0.2 | $ 0.2
Assessment Related premium Payment period | 1 year |  |
Assessment Related loss Payment period | 1 year |  |
Hannover Re and Tokio Millenium Re [Member] |  |  |
New Accounting Pronouncements Or Change In Accounting Principle [Line Items] |  |  |
Reinsurance commutation recepit adjustment | $ 6.3 |  |
Pre-tax loss related to reinsurance commutation | 1.5 |  |
Hannover Re and Allianz Risk Transfer [Member] |  |  |
New Accounting Pronouncements Or Change In Accounting Principle [Line Items] |  |  |
Reinsurance commutation recepit adjustment | $ 9.8 |  |
Buildings [Member] |  |  |
New Accounting Pronouncements Or Change In Accounting Principle [Line Items] |  |  |
Estimated useful life of assets | 39 years |  |
Maximum [Member] |  |  |
New Accounting Pronouncements Or Change In Accounting Principle [Line Items] |  |  |
Short-term investments maturity period | 1 year |  |
Maximum [Member] | Other Fixed Assets [Member] |  |  |
New Accounting Pronouncements Or Change In Accounting Principle [Line Items] |  |  |
Estimated useful life of assets | 7 years |  |
Minimum [Member] |  |  |
New Accounting Pronouncements Or Change In Accounting Principle [Line Items] |  |  |
Short-term investments maturity period | 90 days |  |
Minimum [Member] | Other Fixed Assets [Member] |  |  |
New Accounting Pronouncements Or Change In Accounting Principle [Line Items] |  |  |
Estimated useful life of assets | 3 years |  |

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