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Investments - Additional Information (Detail)
$ in Thousands
 3 Months Ended 9 Months Ended
Sep. 30, 2024
USD ($)
Security
Sep. 30, 2023
USD ($)
Sep. 30, 2024
USD ($)
Security
Sep. 30, 2023
USD ($)
Jun. 30, 2024
USD ($)
Dec. 31, 2023
USD ($)
Marketable Securities [Line Items]            
Individual fixed maturity held in unrealized loss position | Security 132   132      
Number of fixed maturity securities, allowance for credit loss | Security 436   436      
Fixed maturity securities, held-to-maturity, allowance for credit losses $ 136   $ 136   $ 149 $ 182
Available-for-sale, Allowance for Credit Losses 0   0     0
Net realized gains (losses) on investments 158 $ 5,133 (181) $ 5,466    
Net unrealized gains (losses) on equity securities 3,873 $ (7,309) 8,591 $ (3,892)    
Corporate Bonds [Member]            
Marketable Securities [Line Items]            
Fixed maturity securities, held-to-maturity, allowance for credit losses $ 100   $ 100   111 142
Number of majority securities | Security 16   16      
States and Political Subdivisions [Member]            
Marketable Securities [Line Items]            
Fixed maturity securities, held-to-maturity, allowance for credit losses $ 35   $ 35   $ 36 $ 38
Number of majority securities | Security 417   417      
Corporate Fixed Income Securities [Member] | Maximum [Member]            
Marketable Securities [Line Items]            
Investments maturity period using default rate     20 years