Investments - Investment Securities Continuous Unrealized Loss Position (Detail) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Marketable Securities [Line Items]
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months	$ 157,759	$ 40,293
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	8,646	207
Available-for Sale, Fair Value of Investments with Unrealized Losses, 12 Months or Greater	74,761	184,313
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	4,838	11,588
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	232,520	224,606
Available-for Sale, Gross Unrealized Losses, Total	13,484	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	77,323	14,115
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	5,454	111
Available-for Sale, Fair Value of Investments with Unrealized Losses, 12 Months or Greater	22,698	72,358
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	2,132	6,608
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	100,021	86,473
Available-for Sale, Gross Unrealized Losses, Total	7,586	6,719
Corporate Bonds [Member]
Marketable Securities [Line Items]
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months	76,321	26,178
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	2,718	96
Available-for Sale, Fair Value of Investments with Unrealized Losses, 12 Months or Greater	38,179	93,538
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	1,475	3,390
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	114,500	119,716
Available-for Sale, Gross Unrealized Losses, Total	4,193	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	4,115	0
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	474	0
Available-for Sale, Fair Value of Investments with Unrealized Losses, 12 Months or Greater	230	4,745
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	41	445
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	4,345	4,745
Available-for Sale, Gross Unrealized Losses, Total	515	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	13,654	13,672
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	1,190	1,145
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	13,654	13,672
Available-for Sale, Gross Unrealized Losses, Total	$ 1,190	$ 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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