Investments - Investment Securities Continuous Unrealized Loss Position (Detail) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Marketable Securities [Line Items]
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months	$ 95,873	$ 40,293
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	4,693	207
Available-for Sale, Fair Value of Investments with Unrealized Losses, 12 Months or Greater	60,983	184,313
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	3,031	11,588
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	156,856	224,606
Available-for Sale, Gross Unrealized Losses, Total	7,724	11,795
States and Political Subdivisions [Member]
Marketable Securities [Line Items]
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months	61,392	14,115
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	3,595	111
Available-for Sale, Fair Value of Investments with Unrealized Losses, 12 Months or Greater	21,334	72,358
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	1,558	6,608
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	82,726	86,473
Available-for Sale, Gross Unrealized Losses, Total	5,153	6,719
Corporate Bonds [Member]
Marketable Securities [Line Items]
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months	30,359	26,178
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	786	96
Available-for Sale, Fair Value of Investments with Unrealized Losses, 12 Months or Greater	25,343	93,538
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	653	3,390
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	55,702	119,716
Available-for Sale, Gross Unrealized Losses, Total	1,439	3,486
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	4,122	0
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	312	0
Available-for Sale, Fair Value of Investments with Unrealized Losses, 12 Months or Greater	239	4,745
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	29	445
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	4,361	4,745
Available-for Sale, Gross Unrealized Losses, Total	341	445
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	14,067	13,672
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	791	1,145
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	14,067	13,672
Available-for Sale, Gross Unrealized Losses, Total	$ 791	$ 1,145

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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