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, 2022	Dec. 31, 2021
Schedule Of Available For Sale Securities [Line Items]
Within one year, Amortized Cost	$ 30,304	$ 30,925
After one year through five years, Amortized Cost	104,200	97,830
After five years through ten years, Amortized Cost	70,744	58,050
After ten years, Amortized Cost	130,419	129,848
Available-for-sale, Amortized Cost	342,784	324,597
Within one year, Fair Value	30,282	31,258
After one year through five years, Fair Value	103,483	100,716
After five years through ten years, Fair Value	69,143	60,137
After ten years, Fair Value	133,102	141,569
Available-for-sale, Fair Value	342,972	341,769
U.S. Agency-Based Mortgage-Backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Without single maturity date, Amortized Cost	7,117	7,944
Available-for-sale, Amortized Cost	7,117	7,944
Without single maturity date, Fair value	6,962	8,089
Available-for-sale, Fair Value	$ 6,962	$ 8,089