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	Jun. 30, 2026	Mar. 31, 2026	Dec. 31, 2025
Schedule Of Held To Maturity Securities [Line Items]
Held-to-maturity, Amortized Cost, Totals	$ 332,774		$ 350,160
Held-to-Maturity, Allowance for Credit Losses	(60)	$ (65)	(73)
Held-to-maturity, Carrying Amount, Totals	332,714		350,087
Held-to-Maturity, Gross Unrealized Gains	2,188		2,062
Held-to-Maturity, Gross Unrealized Losses	(7,744)		(7,573)
Securities held-to-maturity-fixed maturity, Fair Value	$ 327,158		$ 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	$ 305,868		$ 322,430
Held-to-Maturity, Allowance for Credit Losses	(21)	(22)	(23)
Held-to-maturity, Carrying Amount, Totals	305,847		322,407
Held-to-Maturity, Gross Unrealized Gains	2,175		2,030
Held-to-Maturity, Gross Unrealized Losses	(6,972)		(6,908)
Securities held-to-maturity-fixed maturity, Fair Value	301,050		317,529
Corporate Bonds [Member]
Schedule Of Held To Maturity Securities [Line Items]
Held-to-maturity, Amortized Cost, Totals	16,050		16,751
Held-to-Maturity, Allowance for Credit Losses	(39)	(43)	(50)
Held-to-maturity, Carrying Amount, Totals	16,011		16,701
Held-to-Maturity, Gross Unrealized Gains	0		0
Held-to-Maturity, Gross Unrealized Losses	(446)		(456)
Securities held-to-maturity-fixed maturity, Fair Value	15,565		16,245
U.S. Agency-Based Mortgage-Backed Securities [Member]
Schedule Of Held To Maturity Securities [Line Items]
Held-to-maturity, Amortized Cost, Totals	2,234		2,403
Held-to-maturity, Carrying Amount, Totals	2,234		2,403
Held-to-Maturity, Gross Unrealized Gains	12		26
Held-to-Maturity, Gross Unrealized Losses	(102)		(81)
Securities held-to-maturity-fixed maturity, Fair Value	2,144		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	8,613		8,567
Held-to-maturity, Carrying Amount, Totals	8,613		8,567
Held-to-Maturity, Gross Unrealized Gains	1		6
Held-to-Maturity, Gross Unrealized Losses	(224)		(128)
Securities held-to-maturity-fixed maturity, Fair Value	8,390		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	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

Jun. 30, 2026

Mar. 31, 2026

Dec. 31, 2025

Schedule Of Held To Maturity Securities [Line Items]

Held-to-maturity, Amortized Cost, Totals

$ 332,774

$ 350,160

Held-to-Maturity, Allowance for Credit Losses

(60)

$ (65)

(73)

Held-to-maturity, Carrying Amount, Totals