Investments - Investment Securities Continuous Unrealized Loss Position (Detail) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Marketable Securities [Line Items]
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months	$ 150,460	$ 67,825
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	5,150	657
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	150,460	67,825
Available-for Sale, Gross Unrealized Losses, Total	5,150	657
States and Political Subdivisions [Member]
Marketable Securities [Line Items]
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months	62,574	23,465
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	2,618	240
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	62,574	23,465
Available-for Sale, Gross Unrealized Losses, Total	2,618	240
Corporate Bonds [Member]
Marketable Securities [Line Items]
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months	66,857	36,443
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	1,723	272
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	66,857	36,443
Available-for Sale, Gross Unrealized Losses, Total	1,723	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	6,962	1,146
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	155	13
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	6,962	1,146
Available-for Sale, Gross Unrealized Losses, Total	155	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	14,067	6,771
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	654	132
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	14,067	6,771
Available-for Sale, Gross Unrealized Losses, Total	$ 654	$ 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 less 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 320
-SubTopic 10
-Section 50
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Amount of accumulated unrealized loss on 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.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-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 unrealized loss position without allowance for credit loss.

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