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, 2023	Dec. 31, 2022
Schedule Of Available For Sale Securities [Line Items]
Within one year, Amortized Cost	$ 34,379	$ 28,290
After one year through five years, Amortized Cost	84,849	68,876
After five years through ten years, Amortized Cost	103,517	102,296
After ten years, Amortized Cost	128,436	133,147
Available-for-sale, Amortized Cost	356,984	338,593
Within one year, Fair Value	34,006	27,814
After one year through five years, Fair Value	81,150	65,406
After five years through ten years, Fair Value	99,831	95,366
After ten years, Fair Value	124,766	127,089
Available-for-sale, Fair Value	345,088	321,121
U.S. Agency-Based Mortgage-Backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Without single maturity date, Amortized Cost	5,803	5,984
Without single maturity date, Fair value	$ 5,335	$ 5,446