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Investments - Summary of Carrying Amounts and Fair Value of Investments in Fixed Maturity Securities, Classified as Held-to-Maturity (Detail) - USD ($)
$ in Thousands
Jun. 30, 2026
Dec. 31, 2025
Schedule Of Held To Maturity Securities [Line Items]    
Within one year, Carrying Amount $ 30,276 $ 28,620
After one year through five years, Carrying Amount 71,888 76,161
After five years through ten years, Carrying Amount 115,642 119,321
After ten years, Carrying Amount 112,665 123,573
Held-to-maturity, Carrying Amount, Totals 332,714 350,087
Within one year, Fair Value 30,143 28,561
After one year through five years, Fair Value 69,852 74,506
After five years through ten years, Fair Value 112,707 116,970
After ten years, Fair Value 112,303 122,182
Held-to-maturity, Fair Value, Totals 327,158 344,576
U.S. Agency-Based Mortgage-Backed Securities [Member]    
Schedule Of Held To Maturity Securities [Line Items]    
Without single maturity, Carrying Amount 2,234 2,403
Held-to-maturity, Carrying Amount, Totals 2,234 2,403
Without single maturity, Fair Value 2,144 2,348
Held-to-maturity, Fair Value, Totals 2,144 2,348
Asset-Backed Securities [Member]    
Schedule Of Held To Maturity Securities [Line Items]    
Without single maturity, Carrying Amount 9 9
Held-to-maturity, Carrying Amount, Totals 9 9
Without single maturity, Fair Value 9 9
Held-to-maturity, Fair Value, Totals $ 9 $ 9