Investments - Investment Securities Continuous Unrealized Loss Position (Detail) - USD ($) $ in Thousands	Jun. 30, 2025	Dec. 31, 2024
Marketable Securities [Line Items]
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months	$ 87,828	$ 175,099
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	3,293	7,984
Available-for Sale, Fair Value of Investments with Unrealized Losses, 12 Months or Greater	126,895	60,615
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	8,578	4,637
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	214,723	235,714
Available-for Sale, Gross Unrealized Losses, Total	11,871	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	74,676	100,190
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	3,173	5,748
Available-for Sale, Fair Value of Investments with Unrealized Losses, 12 Months or Greater	70,884	27,446
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	6,419	2,682
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	145,560	127,636
Available-for Sale, Gross Unrealized Losses, Total	9,592	8,430
Corporate Bonds [Member]
Marketable Securities [Line Items]
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months	13,152	71,069
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	120	1,790
Available-for Sale, Fair Value of Investments with Unrealized Losses, 12 Months or Greater	37,848	19,000
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	1,156	993
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	51,000	90,069
Available-for Sale, Gross Unrealized Losses, Total	1,276	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	3,888	219
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	377	40
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	3,888	4,059
Available-for Sale, Gross Unrealized Losses, Total	377	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	14,275	13,950
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	626	922
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	14,275	13,950
Available-for Sale, Gross Unrealized Losses, Total	$ 626	$ 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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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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