Investments - Summary of Carrying Amounts and Fair Value of Investments in Fixed Maturity Securities, Classified as Held-to-Maturity (Detail) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Schedule Of Held To Maturity Securities [Line Items]
Within one year, Carrying Amount	$ 41,878	$ 70,859
After one year through five years, Carrying Amount	165,216	174,157
After five years through ten years, Carrying Amount	121,739	100,543
After ten years, Carrying Amount	159,093	198,945
Held-to-maturity, Carrying Amount, Totals	491,688	549,231
Within one year, Fair Value	41,652	71,455
After one year through five years, Fair Value	159,006	180,376
After five years through ten years, Fair Value	112,665	104,851
After ten years, Fair Value	151,178	214,060
Without single maturity, Fair Value	468,144
Held-to-maturity, Fair Value, Totals	468,144	575,850
U.S. Agency-Based Mortgage-Backed Securities [Member]
Schedule Of Held To Maturity Securities [Line Items]
Without single maturity, Carrying Amount	3,696	4,623
Held-to-maturity, Carrying Amount, Totals	3,696	4,623
Without single maturity, Fair Value	3,576	5,000
Held-to-maturity, Fair Value, Totals	3,576	5,000
Asset-Backed Securities [Member]
Schedule Of Held To Maturity Securities [Line Items]
Without single maturity, Carrying Amount	66	104
Held-to-maturity, Carrying Amount, Totals	66	104
Without single maturity, Fair Value	67	108
Held-to-maturity, Fair Value, Totals	$ 67	$ 108