Investments - Investment Securities Continuous Unrealized Loss Position (Detail) - USD ($) $ in Thousands	Sep. 30, 2025	Dec. 31, 2024
Marketable Securities [Line Items]
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months	$ 44,124	$ 175,099
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	983	7,984
Available-for Sale, Fair Value of Investments with Unrealized Losses, 12 Months or Greater	126,441	60,615
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	7,027	4,637
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	170,565	235,714
Available-for Sale, Gross Unrealized Losses, Total	8,010	12,621
States and Political Subdivisions [Member]
Marketable Securities [Line Items]
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months	35,227	100,190
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	973	5,748
Available-for Sale, Fair Value of Investments with Unrealized Losses, 12 Months or Greater	76,122	27,446
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	5,371	2,682
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	111,349	127,636
Available-for Sale, Gross Unrealized Losses, Total	6,344	8,430
Corporate Bonds [Member]
Marketable Securities [Line Items]
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months	8,897	71,069
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	10	1,790
Available-for Sale, Fair Value of Investments with Unrealized Losses, 12 Months or Greater	32,160	19,000
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	803	993
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	41,057	90,069
Available-for Sale, Gross Unrealized Losses, Total	813	2,783
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	3,840
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	0	446
Available-for Sale, Fair Value of Investments with Unrealized Losses, 12 Months or Greater	3,760	219
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	337	40
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	3,760	4,059
Available-for Sale, Gross Unrealized Losses, Total	337	486
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	14,399	13,950
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	516	922
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	14,399	13,950
Available-for Sale, Gross Unrealized Losses, Total	$ 516	$ 922

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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