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Securities - Additional Information (Detail) - USD ($) $ in Thousands | Sep. 30, 2023 | Dec. 31, 2022
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Schedule Of Marketable Securities [Line Items] |  |
AOCI, Debt Securities, Available-for-sale, Adjustment, Pre Tax | $ 1,300 | $ 1,800
Net unamortized unrealized gain on transferred securities included in accumulated other comprehensive income, net of tax | $ 1,000 | 1,400
Percent Municipal Bond Portfolio Issued By Political Subdivision Or Agencies Within State Of Texas Guaranteed By Texas Permanent School Fund Or Have Been Pre-Refunded | 73.30% |
Debt Securities, Available-for-sale, Allowance for Credit Loss | $ 0 | 0
Held-to-maturity Securities [Member] |  |
Schedule Of Marketable Securities [Line Items] |  |
Carry Value of Securities Pledged | 811,400 | 256,300
Accrued interest receivable | 22,900 | 30,200
Available-for-sale Securities [Member] |  |
Schedule Of Marketable Securities [Line Items] |  |
Carry Value of Securities Pledged | 4,800,000 | 8,000,000
Accrued interest receivable | $ 82,400 | $ 140,600

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- Definition Amount, after tax, of accumulated unrealized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 220 -SubTopic 10 -Name Accounting Standards Codification -Section 45 -Paragraph 14 -Publisher FASB -URI https://asc.fasb.org//1943274/2147482790/220-10-45-14 + Details
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