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, 2021	Dec. 31, 2020
Schedule Of Available For Sale Securities [Line Items]
Within one year, Amortized Cost	$ 30,925	$ 69,177
After one year through five years, Amortized Cost	97,830	80,593
After five years through ten years, Amortized Cost	58,050	53,835
After ten years, Amortized Cost	129,848	165,406
Available-for-sale, Amortized Cost	324,597	387,665
Within one year, Fair Value	31,258	69,938
After one year through five years, Fair Value	100,716	85,829
After five years through ten years, Fair Value	60,137	57,829
After ten years, Fair Value	141,569	181,631
Available-for-sale, Fair Value	341,769	414,279
U.S. Agency-Based Mortgage-Backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Without single maturity date, Amortized Cost	7,944	18,654
Available-for-sale, Amortized Cost	7,944	18,654
Without single maturity date, Fair value	8,089	19,052
Available-for-sale, Fair Value	$ 8,089	$ 19,052