Securities - Additional Information (Detail)	12 Months Ended
Dec. 31, 2021 USD ($) Investment	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Interest Bearing Time Deposits In Banks And Securities [Line Items]
INTEREST-BEARING TIME DEPOSITS IN BANKS	$ 0	$ 0
Interest-bearing time deposits, maturity period, years	12 months
Number of investment positions \| Investment	135
Securities pledged as collateral	$ 3,644,626,000	3,005,084,000
Sales of investment securities available-for-sale	10,631,000	263,042,000	$ 67,414,000
Gross realized gains from security sales	815,000	3,637,000	752,000
Gross realized losses from security sales or calls	$ 0	$ 4,000	$ 19,000
Obligations of State and Political Subdivisions [Member] \| Texas [Member]
Interest Bearing Time Deposits In Banks And Securities [Line Items]
Percentage of securities guaranteed by Texas Permanent School Fund	53.94%	51.57%
Obligations of State and Political Subdivisions [Member] \| Texas [Member] \| Geographic Concentration Risk [Member] \| Available-for-Sale Securities [Member]
Interest Bearing Time Deposits In Banks And Securities [Line Items]
Concentration risk, percentage	72.72%	80.87%

Interest-bearing time deposits in banks.

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Interest Bearing Time Deposits In Banks And Securities [Line Items]

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Percentage of investment portfolio guaranteed by permanent school fund.

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Amount of unrealized gain on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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Number of investments in debt securities 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. Includes beneficial interest in securitized financial asset.

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Amount of restricted investment in debt security measured at fair value with change in fair value recognized in net income (trading).

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Period of time between issuance and maturity of customer deposits, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount of cash inflow from sale of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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