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Investments - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2024 USD ($) ParntershipInvestments Entity	Dec. 31, 2021	Dec. 31, 2023 USD ($)
Schedule Of Available For Sale Securities [Line Items]
Investments in a single issuer as a percentage of shareholders' equity	1.70%		2.10%
Equity securities, at fair value	$ 12,284,000		$ 16,508,000
Weighted average life of fixed maturities securities	5 years
Percentage of book yield due to reinvested to fixed income investments	4.40%	2.20%
Fixed maturity securities with market value	$ 0		0
Investments in insurance enhanced bonds	$ 1,700,000
Insurance enhanced bonds as a percentage of total cash and invested assets	0.10%
Investments in collateralized mortgage obligations, commercial mortgage-backed securities and taxable municipal bonds	$ 1,700,000
Ownership interest exceeds respective investments	3.00%
Number of limited partnership investments | ParntershipInvestments	3
Limited partnership investments with carrying value of fair value	$ 29,400,000		38,200,000
Future Funding Commitments	$ 14,214,000		14,214,000
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	$ 2,600,000		4,000,000.0
Future Funding Commitments	14,200,000		14,200,000
Variable interest entities, maximum exposure to loss	16,800,000		18,300,000
Second VIE that 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	8,900,000		8,200,000
Variable interest entities, maximum exposure to loss	8,900,000		8,200,000
Assured Guaranty Corporation
Schedule Of Available For Sale Securities [Line Items]
Investments in collateralized mortgage obligations, commercial mortgage-backed securities and taxable municipal bonds	800,000
Ambac Financial Group
Schedule Of Available For Sale Securities [Line Items]
Investments in collateralized mortgage obligations, commercial mortgage-backed securities and taxable municipal bonds	900,000
Preferred Stock
Schedule Of Available For Sale Securities [Line Items]
Equity securities, at fair value	12,300,000		$ 16,500,000
U.S. Treasuries
Schedule Of Available For Sale Securities [Line Items]
Gross unrealized losses	784,000
Obligations of States and Political Subdivisions
Schedule Of Available For Sale Securities [Line Items]
Gross unrealized losses	790,000
Mortgage Backed Securities
Schedule Of Available For Sale Securities [Line Items]
Gross unrealized losses	3,284,000
Asset-backed Securities
Schedule Of Available For Sale Securities [Line Items]
Gross unrealized losses	$ 2,882,000
Weighted average credit enhancement	38.70%
Commercial Mortgage-Backed Securities
Schedule Of Available For Sale Securities [Line Items]
Gross unrealized losses	$ 2,488,000
Weighted average credit enhancement	45.40%
Corporate Bonds
Schedule Of Available For Sale Securities [Line Items]
Gross unrealized losses	$ 2,891,000
Foreign Corporate Bonds
Schedule Of Available For Sale Securities [Line Items]
Gross unrealized losses	$ 1,817,000

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