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, 2025	Dec. 31, 2024
Schedule Of Held To Maturity Securities [Line Items]
Within one year, Carrying Amount	$ 28,620	$ 49,303
After one year through five years, Carrying Amount	76,161	93,087
After five years through ten years, Carrying Amount	119,321	115,307
After ten years, Carrying Amount	123,573	152,570
Held-to-maturity, Carrying Amount, Totals	350,087	413,061
Within one year, Fair Value	28,561	48,831
After one year through five years, Fair Value	74,506	89,418
After five years through ten years, Fair Value	116,970	109,812
After ten years, Fair Value	122,182	149,004
Held-to-maturity, Fair Value, Totals	344,576	399,721
U.S. Agency-Based Mortgage-Backed Securities [Member]
Schedule Of Held To Maturity Securities [Line Items]
Without single maturity, Carrying Amount	2,403	2,781
Held-to-maturity, Carrying Amount, Totals	2,403	2,781
Without single maturity, Fair Value	2,348	2,643
Held-to-maturity, Fair Value, Totals	2,348	2,643
Asset-Backed Securities [Member]
Schedule Of Held To Maturity Securities [Line Items]
Without single maturity, Carrying Amount	9	13
Held-to-maturity, Carrying Amount, Totals	9	13
Without single maturity, Fair Value	9	13
Held-to-maturity, Fair Value, Totals	$ 9	$ 13