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	Jun. 30, 2025	Mar. 31, 2025	Dec. 31, 2024
Schedule Of Held To Maturity Securities [Line Items]
Held-to-maturity, Amortized Cost, Totals	$ 384,910		$ 413,177
Held-to-Maturity, Allowance for Credit Losses	(88)	$ (100)	(116)
Held-to-maturity, Carrying Amount, Totals	384,822		413,061
Held-to-Maturity, Gross Unrecognized Gains	629		1,838
Held-to-Maturity, Gross Unrecognized Losses	(14,096)		(15,178)
Securities held-to-maturity-fixed maturity, Fair Value	$ 371,355		$ 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	$ 351,907		$ 368,056
Held-to-Maturity, Allowance for Credit Losses	(27)	(29)	(30)
Held-to-maturity, Carrying Amount, Totals	351,880		368,026
Held-to-Maturity, Gross Unrecognized Gains	593		1,810
Held-to-Maturity, Gross Unrecognized Losses	(13,102)		(13,568)
Securities held-to-maturity-fixed maturity, Fair Value	339,371		356,268
Corporate Bonds [Member]
Schedule Of Held To Maturity Securities [Line Items]
Held-to-maturity, Amortized Cost, Totals	21,899		33,849
Held-to-Maturity, Allowance for Credit Losses	(61)	(71)	(86)
Held-to-maturity, Carrying Amount, Totals	21,838		33,763
Held-to-Maturity, Gross Unrecognized Gains	6		6
Held-to-Maturity, Gross Unrecognized Losses	(697)		(1,099)
Securities held-to-maturity-fixed maturity, Fair Value	21,147		32,670
U.S. Agency-Based Mortgage-Backed Securities [Member]
Schedule Of Held To Maturity Securities [Line Items]
Held-to-maturity, Amortized Cost, Totals	2,573		2,781
Held-to-maturity, Carrying Amount, Totals	2,573		2,781
Held-to-Maturity, Gross Unrecognized Gains	21		11
Held-to-Maturity, Gross Unrecognized Losses	(114)		(149)
Securities held-to-maturity-fixed maturity, Fair Value	2,480		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	8,522		8,478
Held-to-maturity, Carrying Amount, Totals	8,522		8,478
Held-to-Maturity, Gross Unrecognized Gains	9		11
Held-to-Maturity, Gross Unrecognized Losses	(183)		(362)
Securities held-to-maturity-fixed maturity, Fair Value	8,348		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	0
Held-to-maturity, Carrying Amount, Totals	9		13
Securities held-to-maturity-fixed maturity, Fair Value	$ 9		$ 13

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

Jun. 30, 2025

Mar. 31, 2025

Dec. 31, 2024

Schedule Of Held To Maturity Securities [Line Items]

Held-to-maturity, Amortized Cost, Totals

$ 384,910

$ 413,177

Held-to-Maturity, Allowance for Credit Losses

(88)

$ (100)

(116)

Held-to-maturity, Carrying Amount, Totals