Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
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	40 years
Experience rated commission and other operating costs	$ 0.7	$ 1.0	$ 1.7
Pre-tax income related to reinsurance commutation	0.8
Advertising expense	$ 0.3	0.3	$ 0.3
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