Investments - Investment Securities Continuous Unrealized Loss Position (Detail) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Marketable Securities [Line Items]
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months	$ 145,801	$ 40,293
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	7,977	207
Available-for Sale, Fair Value of Investments with Unrealized Losses, 12 Months or Greater	74,087	184,313
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	4,810	11,588
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	219,888	224,606
Available-for Sale, Gross Unrealized Losses, Total	12,787	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	61,604	14,115
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	4,900	111
Available-for Sale, Fair Value of Investments with Unrealized Losses, 12 Months or Greater	25,175	72,358
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	2,113	6,608
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	86,779	86,473
Available-for Sale, Gross Unrealized Losses, Total	7,013	6,719
Corporate Bonds [Member]
Marketable Securities [Line Items]
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months	79,904	26,178
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	2,613	96
Available-for Sale, Fair Value of Investments with Unrealized Losses, 12 Months or Greater	35,075	93,538
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	1,429	3,390
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	114,979	119,716
Available-for Sale, Gross Unrealized Losses, Total	4,042	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	4,293	0
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	464	0
Available-for Sale, Fair Value of Investments with Unrealized Losses, 12 Months or Greater	237	4,745
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	38	445
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	4,530	4,745
Available-for Sale, Gross Unrealized Losses, Total	502	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	13,600	13,672
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	1,230	1,145
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	13,600	13,672
Available-for Sale, Gross Unrealized Losses, Total	$ 1,230	$ 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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