Investments - Summary of Amortized Cost and Fair Value of Investments in Fixed Maturity Securities, Classified as Available-for-Sale (Detail) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Schedule Of Available For Sale Securities [Line Items]
Within one year, Amortized Cost	$ 34,515	$ 28,290
After one year through five years, Amortized Cost	89,175	68,876
After five years through ten years, Amortized Cost	108,099	102,296
After ten years, Amortized Cost	118,283	133,147
Available-for-sale, Amortized Cost	355,670	338,593
Within one year, Fair Value	34,235	27,814
After one year through five years, Fair Value	84,422	65,406
After five years through ten years, Fair Value	103,279	95,366
After ten years, Fair Value	113,386	127,089
Available-for-sale, Fair Value	340,384	321,121
U.S. Agency-Based Mortgage-Backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Without single maturity date, Amortized Cost	5,598	5,984
Without single maturity date, Fair value	$ 5,062	$ 5,446