Fair Value Disclosures - Schedule of Estimated Fair Values and Carrying Values of All Financial Instruments (Detail) - USD ($)	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2022
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	$ 208,277,000	$ 293,286,000	$ 227,298,000
INTEREST-BEARING DEMAND DEPOSITS IN BANKS	180,008,000	37,392,000	138,484,000
Securities available-for-sale, Estimated Fair Value	4,652,537,000	5,474,359,000	5,745,443,000
Loans held-for-investment, net allowance for credit losses	6,904,982,000	6,366,034,000	6,181,380,000
Loans held for sale	12,229,000	11,965,000	18,815,000
Borrowings	751,544,000	642,507,000	774,581,000
IRLCs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset Derivative Fair Value	409,000	400,000	0
Liability Derivative Fair Value	0	0	251,000
Forward Mortgage-Backed Securities Trades [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset Derivative Fair Value	237,000	85,000	1,897,000
Liability Derivative Fair Value	0	0	0
Carrying Value [Member] \| Level 1 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	208,277,000	293,286,000	227,298,000
INTEREST-BEARING DEMAND DEPOSITS IN BANKS	180,008,000	37,392,000	138,484,000
Deposits with no stated maturities	9,712,296,000	10,480,841,000	10,724,016,000
Carrying Value [Member] \| Level 2 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held for sale	12,229,000	11,965,000	18,815,000
Accrued interest receivable	53,518,000	58,162,000	49,416,000
Deposits with stated maturities		524,666,000	418,102,000
Deposits with no stated maturities	1,004,227,000
Borrowings	751,544,000	642,507,000	774,581,000
Accrued interest payable	13,557,000	1,121,000	494,000
Carrying Value [Member] \| Level 2 Inputs [Member] \| IRLCs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset Derivative Fair Value	409,000	400,000	(251,000)
Carrying Value [Member] \| Level 2 Inputs [Member] \| Forward Mortgage-Backed Securities Trades [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liability Derivative Fair Value	237,000	85,000	1,897,000
Carrying Value [Member] \| Levels 1 and 2 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities available-for-sale, Estimated Fair Value	4,652,537,000	5,474,359,000	5,745,443,000
Carrying Value [Member] \| Level 3 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held-for-investment, net allowance for credit losses	6,904,982,000	6,366,034,000	6,181,380,000
Estimated Fair Value [Member] \| Level 1 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	208,277,000	293,286,000	227,298,000
INTEREST-BEARING DEMAND DEPOSITS IN BANKS	180,008,000	37,392,000	138,484,000
Deposits with no stated maturities	9,712,296,000	10,480,841,000	10,724,016,000
Estimated Fair Value [Member] \| Level 2 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held for sale	12,266,000	11,965,000	18,815,000
Accrued interest receivable	53,518,000	58,162,000	49,416,000
Deposits with stated maturities	1,002,893,000	518,811,000	416,400,000
Borrowings	751,544,000	642,507,000	774,581,000
Accrued interest payable	13,557,000	1,121,000	494,000
Estimated Fair Value [Member] \| Level 2 Inputs [Member] \| IRLCs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset Derivative Fair Value	409,000	400,000	(251,000)
Estimated Fair Value [Member] \| Level 2 Inputs [Member] \| Forward Mortgage-Backed Securities Trades [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liability Derivative Fair Value	237,000	85,000	1,897,000
Estimated Fair Value [Member] \| Levels 1 and 2 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities available-for-sale, Estimated Fair Value	4,652,537,000	5,474,359,000	5,745,443,000
Estimated Fair Value [Member] \| Level 3 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held-for-investment, net allowance for credit losses	$ 6,890,218,000	$ 6,372,859,000	$ 6,215,441,000

Accrued interest payable.

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Deposits with no stated maturities.

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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).

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For banks and other depository institutions: Includes cash on hand (currency and coin), cash items in process of collection, noninterest bearing deposits due from other financial institutions (including corporate credit unions), and noninterest bearing balances with the Federal Reserve Banks, Federal Home Loan Banks and central banks.

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Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

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Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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For banks and other depository institutions (including Federal Reserve Banks, if applicable): Interest-bearing deposits in other financial institutions for relatively short periods of time including, for example, certificates of deposits, which are presented separately from cash on the balance sheet.

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Carrying amount as of the balance sheet date of interest earned but not received. Also called accrued interest or accrued interest receivable.

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Amount after allowance and deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements and loans held for sale.

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Amount, after valuation allowance, of financing receivable held for sale and not part of disposal group. Excludes loan covered under loss sharing agreement and loan classified as investment in debt security.

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Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

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Amount of time deposit liabilities, including certificates of deposit.

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