Investments - Additional Information (Detail)	12 Months Ended
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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Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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