Investments - Additional Information (Detail)	9 Months Ended
Sep. 30, 2024 USD ($) Entity ParntershipInvestments	Dec. 31, 2023 USD ($)
Schedule Of Available For Sale Securities [Line Items]
Investments in a single issuer as a percentage of shareholders' equity	1.70%	2.10%
Number of limited partnership investments \| ParntershipInvestments	3
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
Equity securities, at fair value	12,347,000	16,508,000
Future Funding Commitments	14,214,000	14,214,000
Limited partnership investments with carrying value of fair value	$ 29,500,000	38,200,000
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	$ 3,400,000	4,000,000
Future Funding Commitments	14,200,000	14,200,000
Variable interest entities, maximum exposure to loss	17,600,000	18,300,000
Second 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	8,600,000	8,200,000
Variable interest entities, maximum exposure to loss	8,600,000	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
Other Assets
Schedule Of Available For Sale Securities [Line Items]
Accrued interest receivable related to fixed maturities	3,500,000	7,500,000
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	683,000
Obligations of States and Political Subdivisions
Schedule Of Available For Sale Securities [Line Items]
Gross unrealized losses	634,000
Mortgage Backed Securities
Schedule Of Available For Sale Securities [Line Items]
Gross unrealized losses	2,438,000
Asset-backed Securities
Schedule Of Available For Sale Securities [Line Items]
Gross unrealized losses	$ 2,810,000
Weighted average credit enhancement	38.00%
Commercial Mortgage-Backed Securities
Schedule Of Available For Sale Securities [Line Items]
Gross unrealized losses	$ 2,526,000
Weighted average credit enhancement	44.00%
Corporate Bonds
Schedule Of Available For Sale Securities [Line Items]
Gross unrealized losses	$ 2,777,000
Foreign Corporate Bonds
Schedule Of Available For Sale Securities [Line Items]
Gross unrealized losses	$ 1,604,000

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