Investments - Gross Unrecognized Gains and Losses and Cost or Amortized Cost, Allowance for Credit Losses, Carrying Amount and Fair Value of Investments Classified as Held-to-Maturity (Detail) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Schedule Of Held To Maturity Securities [Line Items]
Held-to-maturity, Amortized Cost, Totals	$ 413,177	$ 483,757
Held-to-Maturity, Allowance for Credit Losses	(116)	(182)
Held-to-Maturity, Carrying Amount	413,061	483,575
Held-to-Maturity, Gross Unrecognized Gains	1,838	4,218
Held-to-Maturity, Gross Unrecognized Losses	(15,178)	(14,701)
Securities held-to-maturity-fixed maturity, Fair Value	$ 399,721	$ 473,092
Investment, Type [Extensible Enumeration]	U.S. Agency-Based Mortgage-Backed Securities [Member]	U.S. Agency-Based Mortgage-Backed Securities [Member]
States and Political Subdivisions [Member]
Schedule Of Held To Maturity Securities [Line Items]
Held-to-maturity, Amortized Cost, Totals	$ 368,056	$ 416,916
Held-to-Maturity, Allowance for Credit Losses	(30)	(38)
Held-to-Maturity, Carrying Amount	368,026	416,878
Held-to-Maturity, Gross Unrecognized Gains	1,810	4,166
Held-to-Maturity, Gross Unrecognized Losses	(13,568)	(12,074)
Securities held-to-maturity-fixed maturity, Fair Value	356,268	408,970
Corporate Bonds [Member]
Schedule Of Held To Maturity Securities [Line Items]
Held-to-maturity, Amortized Cost, Totals	33,849	52,321
Held-to-Maturity, Allowance for Credit Losses	(86)	(142)
Held-to-Maturity, Carrying Amount	33,763	52,179
Held-to-Maturity, Gross Unrecognized Gains	6
Held-to-Maturity, Gross Unrecognized Losses	(1,099)	(2,231)
Securities held-to-maturity-fixed maturity, Fair Value	32,670	49,948
U.S. Agency-Based Mortgage-Backed Securities [Member]
Schedule Of Held To Maturity Securities [Line Items]
Held-to-maturity, Amortized Cost, Totals	2,781	3,297
Held-to-Maturity, Carrying Amount	2,781	3,297
Held-to-Maturity, Gross Unrecognized Gains	11	25
Held-to-Maturity, Gross Unrecognized Losses	(149)	(123)
Securities held-to-maturity-fixed maturity, Fair Value	2,643	3,199
U.S. Treasury Securities and Obligations of U.S. Government Agencies [Member]
Schedule Of Held To Maturity Securities [Line Items]
Held-to-maturity, Amortized Cost, Totals	8,478	11,186
Held-to-Maturity, Carrying Amount	8,478	11,186
Held-to-Maturity, Gross Unrecognized Gains	11	26
Held-to-Maturity, Gross Unrecognized Losses	(362)	(273)
Securities held-to-maturity-fixed maturity, Fair Value	8,127	10,939
Asset-Backed Securities [Member]
Schedule Of Held To Maturity Securities [Line Items]
Held-to-maturity, Amortized Cost, Totals	13	37
Held-to-Maturity, Allowance for Credit Losses		(2)
Held-to-Maturity, Carrying Amount	13	35
Held-to-Maturity, Gross Unrecognized Gains		1
Securities held-to-maturity-fixed maturity, Fair Value	$ 13	$ 36

Investments - Gross Unrecognized Gains and Losses and Cost or Amortized Cost, Allowance for Credit Losses, Carrying Amount and Fair Value of Investments Classified as Held-to-Maturity (Detail) - USD ($)
$ in Thousands

Dec. 31, 2024

Dec. 31, 2023

Schedule Of Held To Maturity Securities [Line Items]

Held-to-maturity, Amortized Cost, Totals

$ 413,177

$ 483,757

Held-to-Maturity, Allowance for Credit Losses

(116)

(182)

Held-to-Maturity, Carrying Amount

413,061

483,575