Investments - Investment Securities Continuous Unrealized Loss Position (Detail) - USD ($) $ in Thousands	Sep. 30, 2026	Dec. 31, 2025
Marketable Securities [Line Items]
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months	$ 174,439	$ 34,429
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	9,835	642
Available-for Sale, Fair Value of Investments with Unrealized Losses, 12 Months or Greater	79,060	123,699
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	11,073	6,297
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	253,499	158,128
Available-for Sale, Gross Unrealized Losses, Total	20,908	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	91,781	28,892
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	7,046	634
Available-for Sale, Fair Value of Investments with Unrealized Losses, 12 Months or Greater	54,097	76,440
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	9,103	4,848
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	145,878	105,332
Available-for Sale, Gross Unrealized Losses, Total	16,149	5,482
Corporate Bonds [Member]
Marketable Securities [Line Items]
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months	79,215	5,537
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	2,380	8
Available-for Sale, Fair Value of Investments with Unrealized Losses, 12 Months or Greater	17,461	31,115
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	983	717
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	96,676	36,652
Available-for Sale, Gross Unrealized Losses, Total	3,363	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	3,060	3,641
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	477	305
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	3,060	3,641
Available-for Sale, Gross Unrealized Losses, Total	477	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	3,443	0
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	409	0
Available-for Sale, Fair Value of Investments with Unrealized Losses, 12 Months or Greater	4,442	12,503
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	510	427
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	7,885	12,503
Available-for Sale, Gross Unrealized Losses, Total	$ 919	$ 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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