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, 2025	Dec. 31, 2024
Schedule Of Held To Maturity Securities [Line Items]
Held-to-maturity, Amortized Cost, Totals	$ 350,160	$ 413,177
Held-to-Maturity, Allowance for Credit Losses	(73)	(116)
Held-to-maturity, Carrying Amount, Totals	350,087	413,061
Held-to-Maturity, Gross Unrecognized Gains	2,062	1,838
Held-to-Maturity, Gross Unrecognized Losses	(7,573)	(15,178)
Securities held-to-maturity-fixed maturity, Fair Value	$ 344,576	$ 399,721
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	$ 322,430	$ 368,056
Held-to-Maturity, Allowance for Credit Losses	(23)	(30)
Held-to-maturity, Carrying Amount, Totals	322,407	368,026
Held-to-Maturity, Gross Unrecognized Gains	2,030	1,810
Held-to-Maturity, Gross Unrecognized Losses	(6,908)	(13,568)
Securities held-to-maturity-fixed maturity, Fair Value	317,529	356,268
Corporate Bonds [Member]
Schedule Of Held To Maturity Securities [Line Items]
Held-to-maturity, Amortized Cost, Totals	16,751	33,849
Held-to-Maturity, Allowance for Credit Losses	(50)	(86)
Held-to-maturity, Carrying Amount, Totals	16,701	33,763
Held-to-Maturity, Gross Unrecognized Gains		6
Held-to-Maturity, Gross Unrecognized Losses	(456)	(1,099)
Securities held-to-maturity-fixed maturity, Fair Value	16,245	32,670
U.S. Agency-Based Mortgage-Backed Securities [Member]
Schedule Of Held To Maturity Securities [Line Items]
Held-to-maturity, Amortized Cost, Totals	2,403	2,781
Held-to-maturity, Carrying Amount, Totals	2,403	2,781
Held-to-Maturity, Gross Unrecognized Gains	26	11
Held-to-Maturity, Gross Unrecognized Losses	(81)	(149)
Securities held-to-maturity-fixed maturity, Fair Value	2,348	2,643
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	8,567	8,478
Held-to-maturity, Carrying Amount, Totals	8,567	8,478
Held-to-Maturity, Gross Unrecognized Gains	6	11
Held-to-Maturity, Gross Unrecognized Losses	(128)	(362)
Securities held-to-maturity-fixed maturity, Fair Value	8,445	8,127
Asset-Backed Securities [Member]
Schedule Of Held To Maturity Securities [Line Items]
Held-to-maturity, Amortized Cost, Totals	9	13
Held-to-Maturity, Allowance for Credit Losses	0	0
Held-to-maturity, Carrying Amount, Totals	9	13
Held-to-Maturity, Gross Unrecognized Gains		0
Securities held-to-maturity-fixed maturity, Fair Value	$ 9	$ 13