Investments - Investment Securities Continuous Unrealized Loss Position (Detail) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Marketable Securities [Line Items]
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months	$ 146,022	$ 196,433
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	3,198	10,625
Available-for Sale, Fair Value of Investments with Unrealized Losses, 12 Months or Greater	131,884	63,424
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	13,176	7,849
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	277,906	259,857
Available-for Sale, Gross Unrealized Losses, Total	16,374	18,474
States and Political Subdivisions [Member]
Marketable Securities [Line Items]
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months	46,548	87,522
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	441	5,319
Available-for Sale, Fair Value of Investments with Unrealized Losses, 12 Months or Greater	62,315	24,980
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	7,899	4,507
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	108,863	112,502
Available-for Sale, Gross Unrealized Losses, Total	8,340	9,826
Corporate Bonds [Member]
Marketable Securities [Line Items]
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months	98,553	98,590
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	2,755	4,549
Available-for Sale, Fair Value of Investments with Unrealized Losses, 12 Months or Greater	51,149	30,011
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	3,311	2,108
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	149,702	128,601
Available-for Sale, Gross Unrealized Losses, Total	6,066	6,657
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		4,732
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months		444
Available-for Sale, Fair Value of Investments with Unrealized Losses, 12 Months or Greater	5,062	714
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	536	94
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	5,062	5,446
Available-for Sale, Gross Unrealized Losses, Total	536	538
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	921	5,589
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	2	313
Available-for Sale, Fair Value of Investments with Unrealized Losses, 12 Months or Greater	13,358	7,719
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	1,430	1,140
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	14,279	13,308
Available-for Sale, Gross Unrealized Losses, Total	$ 1,432	$ 1,453

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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