Fair Value Disclosures - Schedule of Estimated Fair Values and Carrying Values of All Financial Instruments (Detail) - USD ($)	Mar. 31, 2026	Dec. 31, 2025
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	$ 264,850,000	$ 249,466,000
FEDERAL FUNDS SOLD	14,075,000	1,575,000
INTEREST-BEARING DEMAND DEPOSITS IN BANKS	458,203,000	826,947,000
Available-for-sale securities	5,668,792,000	5,514,113,000
Loans held-for-investment, net of allowance for credit losses	8,177,202,000	8,052,740,000
Loans held for sale	22,984,000	29,992,000
Borrowings	22,306,000	21,680,000
IRLCs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
IRLCs	723,000	579,000
Forward mortgage-backed securities trades asset (liability)	0	0
Forward Mortgage-Backed Securities Trades [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
IRLCs	515,000	0
Forward mortgage-backed securities trades asset (liability)	0	132,000
Carrying Value [Member] \| Level 1 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	264,850,000	249,466,000
FEDERAL FUNDS SOLD	14,075,000	1,575,000
INTEREST-BEARING DEMAND DEPOSITS IN BANKS	458,203,000	826,947,000
Deposits with no stated maturities	12,348,257,000	12,444,975,000
Carrying Value [Member] \| Level 2 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held for sale	22,984,000	29,992,000
Accrued interest receivable	62,799,000	68,470,000
Deposits with stated maturities	896,980,000	900,554,000
Repurchase Agreements	67,946,000	62,956,000
Borrowings	22,306,000	21,680,000
Accrued interest payable	5,120,000	5,673,000
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)	515,000	(132,000)
Carrying Value [Member] \| Levels 1 and 2 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale securities	5,668,792,000	5,514,113,000
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	8,177,202,000	8,052,740,000
Carrying Value [Member] \| Level 3 Inputs [Member] \| IRLCs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
IRLCs	723,000	579,000
Estimated Fair Value [Member] \| Level 1 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	264,850,000	249,466,000
FEDERAL FUNDS SOLD	14,075,000	1,575,000
INTEREST-BEARING DEMAND DEPOSITS IN BANKS	458,203,000	826,947,000
Deposits with no stated maturities	12,348,257,000	12,444,975,000
Estimated Fair Value [Member] \| Level 2 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held for sale	23,136,000	30,163,000
Accrued interest receivable	62,799,000	68,470,000
Deposits with stated maturities	892,425,000	902,588,000
Repurchase Agreements	67,946,000	62,956,000
Borrowings	22,306,000	21,680,000
Accrued interest payable	5,120,000	5,673,000
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)	515,000	(132,000)
Estimated Fair Value [Member] \| Levels 1 and 2 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale securities	5,668,792,000	5,514,113,000
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	8,139,550,000	8,061,186,000
Estimated Fair Value [Member] \| Level 3 Inputs [Member] \| IRLCs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
IRLCs	$ 723,000	$ 579,000

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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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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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