Investments - Summary of Amortized Cost and Fair Value of Investments in Fixed Maturity Securities, Classified as Available-for-Sale (Detail) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Schedule Of Available For Sale Securities [Line Items]
Within one year, Amortized Cost	$ 25,995	$ 28,290
After one year through five years, Amortized Cost	106,178	68,876
After five years through ten years, Amortized Cost	82,664	102,296
After ten years, Amortized Cost	106,144	133,147
Without single maturity date, Amortized Cost	$ 5,190	$ 5,984
Investment, Type [Extensible Enumeration]	Mortgage-Backed Securities, Issued by US Government Sponsored Enterprises [Member]	Mortgage-Backed Securities, Issued by US Government Sponsored Enterprises [Member]
Available-for-sale, Amortized Cost	$ 326,171	$ 338,593
Within one year, Fair Value	25,875	27,814
After one year through five years, Fair Value	102,201	65,406
After five years through ten years, Fair Value	80,911	95,366
After ten years, Fair Value	103,332	127,089
Without single maturity date, Fair value	4,745	5,446
Available-for-sale, Fair Value	$ 317,064	$ 321,121