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, 2022	Dec. 31, 2021
Schedule Of Available For Sale Securities [Line Items]
Within one year, Amortized Cost	$ 28,290	$ 30,925
After one year through five years, Amortized Cost	68,876	97,830
After five years through ten years, Amortized Cost	102,296	58,050
After ten years, Amortized Cost	133,147	129,848
Available-for-sale, Amortized Cost	338,593	324,597
Within one year, Fair Value	27,814	31,258
After one year through five years, Fair Value	65,406	100,716
After five years through ten years, Fair Value	95,366	60,137
After ten years, Fair Value	127,089	141,569
Available-for-sale, Fair Value	321,121	341,769
U.S. Agency-Based Mortgage-Backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Without single maturity date, Amortized Cost	5,984	7,944
Without single maturity date, Fair value	$ 5,446	$ 8,089