Investments - Summary of Amortized Cost and Fair Value of Investments in Fixed Maturity Securities, Classified as Available-for-Sale (Detail) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Schedule Of Available For Sale Securities [Line Items]
Within one year, Amortized Cost	$ 19,402	$ 25,995
After one year through five years, Amortized Cost	107,593	106,178
After five years through ten years, Amortized Cost	74,338	82,664
After ten years, Amortized Cost	95,326	106,144
Without single maturity date, Amortized Cost	$ 5,032	$ 5,190
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	$ 301,691	$ 326,171
Within one year, Fair Value	19,297	25,875
After one year through five years, Fair Value	103,291	102,201
After five years through ten years, Fair Value	71,695	80,911
After ten years, Fair Value	91,860	103,332
Without single maturity date, Fair value	4,530	4,745
Available-for-sale, Fair Value	$ 290,673	$ 317,064