Fair Value Measurements - Estimated Fair Values of Company's Financial Instruments (Detail) - USD ($) $ in Thousands	Mar. 31, 2025	Dec. 31, 2024	Mar. 31, 2024
FINANCIAL ASSETS
Federal funds sold, Carrying Amount	$ 520	$ 715
Debt securities held for investment, Carrying Amount	777	837
Loans, net of allowance for credit losses, Carrying Amount	7,994,072	7,925,613
Debt securities held for investment, Fair Value	777	837
Loans held for sale, Fair Value	8,283	8,073
FINANCIAL LIABILITIES
Deposits, Carrying Amount	12,126,750	11,718,546	$ 10,909,621
Subordinated debt, Carrying Amount	86,171	86,157
OFF-BALANCE SHEET FINANCIAL INSTRUMENTS
Loan commitments, Fair Value	4,290	4,313
Letters of credit, Fair Value	716	769
Level 2 Inputs [Member]
FINANCIAL ASSETS
Cash and cash equivalents, Carrying Amount	3,974,172	3,553,772
Federal funds sold, Carrying Amount	520	715
Debt securities held for investment, Carrying Amount	775	2
Loans held for sale, Carrying Amount	8,283	8,073
Cash and cash equivalents, Fair Value	3,974,172	3,553,772
Federal funds sold, Fair Value	520	715
Debt securities held for investment, Fair Value	775	2
Loans held for sale, Fair Value	8,283	8,073
FINANCIAL LIABILITIES
Deposits, Carrying Amount	12,126,750	11,718,546
Subordinated debt, Carrying Amount	86,171	86,157
Deposits, Fair Value	11,451,560	10,966,958
Subordinated debt, Fair Value	79,800	77,998
Level 3 Inputs [Member]
FINANCIAL ASSETS
Debt securities held for investment, Carrying Amount	2	835
Loans, net of allowance for credit losses, Carrying Amount	7,994,072	7,925,613
Debt securities held for investment, Fair Value	2	835
Loans, net of allowance for credit losses, Fair Value	$ 8,792,307	$ 8,643,418

Financial instruments off balance sheet.

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Letters of credit fair value disclosure.

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Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Fair value portion of arrangements with third parties, including, but not limited to, operating lease arrangement and arrangement in which the entity has agreed to expend funds to procure goods or services, or has agreed to commit resources to supply goods or services.

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The aggregate of all deposit liabilities held by the entity, including foreign and domestic, interest and noninterest bearing; may include demand deposits, saving deposits, Negotiable Order of Withdrawal (NOW) and time deposits among others.

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Fair value portion of deposit liabilities held by the entity, including, but not limited to, foreign and domestic, interest and noninterest bearing, demand deposits, saving deposits, negotiable orders of withdrawal (NOW) and time deposits.

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Fair value of subordinated debt obligations including, but not limited to, subordinated loan, subordinated bond, subordinated debenture or junior debt.

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The amount outstanding of funds lent to other depository institutions, securities brokers, or securities dealers in the form of Federal Funds sold; for example, immediately available funds lent under agreements or contracts that mature in one business day or roll over under a continuing contract, regardless of the nature of the transaction or the collateral involved, excluding overnight lending for commercial and industrial purposes. Also include Federal Funds sold under agreements to resell on a gross basis, excluding (1) sales of term Federal Funds, (2) due bills representing purchases of securities or other assets by the reporting bank that have not yet been delivered and similar instruments, (3) resale agreements that mature in more than one business day involving assets other than securities, and (4) yield maintenance dollar repurchase agreements.

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Fair value portion of federal funds sold and securities borrowed or purchased under agreements to resell.

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Amount, before allowance for credit loss, of investment in debt security measured at amortized cost (held-to-maturity).

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Fair value of investment in debt security measured at amortized cost (held-to-maturity).

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Fair value portion of loans held-for-sale including, but not limited to, mortgage loans and finance receivables.

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Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

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Amount, before valuation allowance, of financing receivable classified as held-for-sale.

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Amortized cost, after allowance for credit loss, of financing receivable. Excludes financing receivable covered under loss sharing agreement and net investment in lease.

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Including the current and noncurrent portions, carrying value as of the balance sheet date of subordinated debt (with initial maturities beyond one year or beyond the operating cycle if longer). Subordinated debt places a lender in a lien position behind debt having a higher priority of repayment in liquidation of the entity's assets.

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