Investments - Gross Unrealized 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	Mar. 31, 2026	Dec. 31, 2025
Schedule Of Held To Maturity Securities [Line Items]
Held-to-maturity, Amortized Cost, Totals	$ 340,611	$ 350,160
Held-to-Maturity, Allowance for Credit Losses	(65)	(73)
Held-to-maturity, Carrying Amount, Totals	340,546	350,087
Held-to-Maturity, Gross Unrealized Gains	1,120	2,062
Held-to-Maturity, Gross Unrealized Losses	(9,007)	(7,573)
Securities held-to-maturity-fixed maturity, Fair Value	$ 332,659	$ 344,576
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	$ 313,513	$ 322,430
Held-to-Maturity, Allowance for Credit Losses	(22)	(23)
Held-to-maturity, Carrying Amount, Totals	313,491	322,407
Held-to-Maturity, Gross Unrealized Gains	1,101	2,030
Held-to-Maturity, Gross Unrealized Losses	(8,241)	(6,908)
Securities held-to-maturity-fixed maturity, Fair Value	306,351	317,529
Corporate Bonds [Member]
Schedule Of Held To Maturity Securities [Line Items]
Held-to-maturity, Amortized Cost, Totals	16,184	16,751
Held-to-Maturity, Allowance for Credit Losses	(43)	(50)
Held-to-maturity, Carrying Amount, Totals	16,141	16,701
Held-to-Maturity, Gross Unrealized Gains	0	0
Held-to-Maturity, Gross Unrealized Losses	(488)	(456)
Securities held-to-maturity-fixed maturity, Fair Value	15,653	16,245
U.S. Agency-Based Mortgage-Backed Securities [Member]
Schedule Of Held To Maturity Securities [Line Items]
Held-to-maturity, Amortized Cost, Totals	2,315	2,403
Held-to-maturity, Carrying Amount, Totals	2,315	2,403
Held-to-Maturity, Gross Unrealized Gains	16	26
Held-to-Maturity, Gross Unrealized Losses	(93)	(81)
Securities held-to-maturity-fixed maturity, Fair Value	2,238	2,348
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	8,590	8,567
Held-to-maturity, Carrying Amount, Totals	8,590	8,567
Held-to-Maturity, Gross Unrealized Gains	3	6
Held-to-Maturity, Gross Unrealized Losses	(185)	(128)
Securities held-to-maturity-fixed maturity, Fair Value	8,408	8,445
Asset-Backed Securities [Member]
Schedule Of Held To Maturity Securities [Line Items]
Held-to-maturity, Amortized Cost, Totals	9	9
Held-to-Maturity, Allowance for Credit Losses	0	0
Held-to-maturity, Carrying Amount, Totals	9	9
Securities held-to-maturity-fixed maturity, Fair Value	$ 9	$ 9

Investments - Gross Unrealized 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

Mar. 31, 2026

Dec. 31, 2025

Schedule Of Held To Maturity Securities [Line Items]

Held-to-maturity, Amortized Cost, Totals

$ 340,611

$ 350,160

Held-to-Maturity, Allowance for Credit Losses

(65)

(73)

Held-to-maturity, Carrying Amount, Totals

340,546

350,087