Fair Value Disclosures - Schedule of Estimated Fair Values and Carrying Values of All Financial Instruments (Detail) - USD ($)	3 Months Ended	12 Months Ended
Mar. 31, 2025	Mar. 31, 2024	Dec. 31, 2024
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	$ 232,943,000	$ 222,464,000	$ 259,996,000
Federal funds sold	11,750,000	12,300,000	0
Interest-bearing demand deposits in banks	682,362,000	365,397,000	503,417,000
Available-for-sale securities	4,760,431,000	4,658,526,000	4,617,759,000
Loans held-for-investment, net of allowance for credit losses	7,844,531,000	7,139,848,000	7,814,773,000
Loans held for sale	14,348,000	16,109,000	8,235,000
Borrowings	26,978,000	26,803,000	135,603,000
IRLCs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
IRLCs	603,000	803,000	238,000
Forward mortgage-backed securities trades asset (liability)	0	0	0
Forward Mortgage-Backed Securities Trades [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
IRLCs	0	0	84,000
Forward mortgage-backed securities trades asset (liability)	202,000	91,000	0
Carrying Value [Member] \| Level 1 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	232,943,000	222,464,000	259,996,000
Federal funds sold	11,750,000	12,300,000	0
Interest-bearing demand deposits in banks	682,362,000	365,397,000	503,417,000
Deposits with no stated maturities	11,563,649,000	10,351,267,000	11,181,898,000
Carrying Value [Member] \| Level 2 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held for sale	14,348,000	16,109,000	8,235,000
Accrued interest receivable	58,491,000	56,278,000	60,749,000
Deposits with stated maturities	903,122,000	938,541,000	917,276,000
Repurchase Agreements	56,606,000	307,297,000	61,416,000
Borrowings	26,978,000	26,803,000	135,603,000
Accrued interest payable	6,536,000	8,362,000	6,909,000
Carrying Value [Member] \| Level 2 Inputs [Member] \| Forward Mortgage-Backed Securities Trades [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Forward mortgage-backed securities trades asset (liability)	(202,000)	(91,000)	84,000
Carrying Value [Member] \| Levels 1 and 2 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale securities	4,760,431,000	4,658,526,000	4,617,759,000
Carrying Value [Member] \| Level 3 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held-for-investment, net of allowance for credit losses	7,844,531,000	7,139,847,000	7,814,773,000
Carrying Value [Member] \| Level 3 Inputs [Member] \| IRLCs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
IRLCs	603,000	803,000	238,000
Estimated Fair Value [Member] \| Level 1 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	232,943,000	222,464,000	259,996,000
Federal funds sold	11,750,000	12,300,000	0
Interest-bearing demand deposits in banks	682,362,000	365,397,000	503,417,000
Deposits with no stated maturities	11,563,649,000	10,351,267,000	11,181,898,000
Estimated Fair Value [Member] \| Level 2 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held for sale	14,349,000	16,109,000	8,276,000
Accrued interest receivable	58,491,000	56,278,000	60,749,000
Deposits with stated maturities	904,900,000	938,459,000	919,774,000
Repurchase Agreements	56,606,000	307,297,000	61,416,000
Borrowings	26,978,000	26,803,000	135,603,000
Accrued interest payable	6,536,000	8,362,000	6,909,000
Estimated Fair Value [Member] \| Level 2 Inputs [Member] \| Forward Mortgage-Backed Securities Trades [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Forward mortgage-backed securities trades asset (liability)	(202,000)	(91,000)	84,000
Estimated Fair Value [Member] \| Levels 1 and 2 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale securities	4,760,431,000	4,658,526,000	4,617,759,000
Estimated Fair Value [Member] \| Level 3 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held-for-investment, net of allowance for credit losses	7,874,001,000	7,141,043,000	7,806,258,000
Estimated Fair Value [Member] \| Level 3 Inputs [Member] \| IRLCs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
IRLCs	$ 603,000	$ 803,000	$ 238,000

Accrued interest payable.

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Deposits with no stated maturities.

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Loan And Leases Receivable Net Reported Amount

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Repurchase Agreements

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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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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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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 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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