Investments - Summary of Amortized Cost and Fair Value of Investments in Fixed Maturity Securities, Classified as Available-for-Sale (Detail) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Schedule Of Available For Sale Securities [Line Items]
Within one year, Amortized Cost	$ 38,171	$ 30,925
After one year through five years, Amortized Cost	71,031	97,830
After five years through ten years, Amortized Cost	100,619	58,050
After ten years, Amortized Cost	135,089	129,848
Available-for-sale, Amortized Cost	351,118	324,597
Within one year, Fair Value	37,570	31,258
After one year through five years, Fair Value	67,053	100,716
After five years through ten years, Fair Value	91,651	60,137
After ten years, Fair Value	124,038	141,569
Available-for-sale, Fair Value	325,891	341,769
U.S. Agency-Based Mortgage-Backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Without single maturity date, Amortized Cost	6,208	7,944
Without single maturity date, Fair value	$ 5,579	$ 8,089