Investments - Investment Securities Continuous Unrealized Loss Position (Detail) - USD ($) $ in Thousands	Mar. 31, 2026	Dec. 31, 2025
Marketable Securities [Line Items]
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months	$ 120,866	$ 34,429
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	1,817	642
Available-for Sale, Fair Value of Investments with Unrealized Losses, 12 Months or Greater	96,723	123,699
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	6,900	6,297
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	217,589	158,128
Available-for Sale, Gross Unrealized Losses, Total	8,717	6,939
States and Political Subdivisions [Member]
Marketable Securities [Line Items]
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months	67,158	28,892
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	1,536	634
Available-for Sale, Fair Value of Investments with Unrealized Losses, 12 Months or Greater	59,936	76,440
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	5,351	4,848
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	127,094	105,332
Available-for Sale, Gross Unrealized Losses, Total	6,887	5,482
Corporate Bonds [Member]
Marketable Securities [Line Items]
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months	53,708	5,537
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	281	8
Available-for Sale, Fair Value of Investments with Unrealized Losses, 12 Months or Greater	26,777	31,115
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	807	717
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	80,485	36,652
Available-for Sale, Gross Unrealized Losses, Total	1,088	725
U.S. Agency-Based Mortgage-Backed Securities [Member]
Marketable Securities [Line Items]
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months	0	0
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	0	0
Available-for Sale, Fair Value of Investments with Unrealized Losses, 12 Months or Greater	3,494	3,641
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	317	305
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	3,494	3,641
Available-for Sale, Gross Unrealized Losses, Total	317	305
U.S. Treasury Securities and Obligations of U.S. Government Agencies [Member]
Marketable Securities [Line Items]
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months	0	0
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	0	0
Available-for Sale, Fair Value of Investments with Unrealized Losses, 12 Months or Greater	6,516	12,503
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	425	427
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	6,516	12,503
Available-for Sale, Gross Unrealized Losses, Total	$ 425	$ 427

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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