Investments - Investment Securities Continuous Unrealized Loss Position (Detail) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Marketable Securities [Line Items]
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months	$ 288,084	$ 67,825
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	20,141	657
Available-for Sale, Fair Value of Investments with Unrealized Losses, 12 Months or Greater	34,574
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	5,210
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	322,658	67,825
Available-for Sale, Gross Unrealized Losses, Total	25,351	657
States and Political Subdivisions [Member]
Marketable Securities [Line Items]
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months	150,390	23,465
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	11,587	240
Available-for Sale, Fair Value of Investments with Unrealized Losses, 12 Months or Greater	13,456
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	2,614
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	163,846	23,465
Available-for Sale, Gross Unrealized Losses, Total	14,201	240
Corporate Bonds [Member]
Marketable Securities [Line Items]
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months	124,596	36,443
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	7,146	272
Available-for Sale, Fair Value of Investments with Unrealized Losses, 12 Months or Greater	15,452
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	1,814
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	140,048	36,443
Available-for Sale, Gross Unrealized Losses, Total	8,960	272
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	5,120	1,146
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	558	13
Available-for Sale, Fair Value of Investments with Unrealized Losses, 12 Months or Greater	458
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	71
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	5,578	1,146
Available-for Sale, Gross Unrealized Losses, Total	629	13
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	7,978	6,771
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	850	132
Available-for Sale, Fair Value of Investments with Unrealized Losses, 12 Months or Greater	5,208
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	711
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	13,186	6,771
Available-for Sale, Gross Unrealized Losses, Total	$ 1,561	$ 132

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.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 50
-Paragraph 5
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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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 less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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