Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2026	Dec. 31, 2025
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	$ 24,205	$ 22,331
Available-for-sale securities	13,660,886	13,709,141
Derivative Assets, Fair Value	266,599	281,329
Derivative Liabilities, Fair Value	146,429	136,452
Securities sold not yet purchased	8,300	4,100
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	7,513	5,145
Available-for-sale securities	2,397,394	2,497,930
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	16,692	17,186
Available-for-sale securities	11,263,492	11,211,211
U.S. Treasury [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	2,257,713	2,320,815
U.S. Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	49,968	62,370
Mortgage-backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	8,287,873	8,167,873
State and political subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	2,371,456	2,446,588
Corporates [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	139,681	177,115
Fair Value Measurement, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	24,205	22,331
Available-for-sale securities	13,660,886	13,709,141
Equity securities with readily determinable fair values	12,604	14,690
Derivative Assets, Fair Value	266,599	281,329
Total	13,964,294	14,027,491
Derivative Liabilities, Fair Value	146,429	136,452
Securities sold not yet purchased	8,290	4,052
Total	154,719	140,504
Fair Value Measurement, Recurring [Member] \| Collateralized loan obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	554,195	534,380
Fair Value Measurement, Recurring [Member] \| Trading - other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	427	317
Fair Value Measurement, Recurring [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	7,513	5,145
Available-for-sale securities	2,397,394	2,497,930
Equity securities with readily determinable fair values	12,604	14,690
Total	2,417,511	2,517,765
Fair Value Measurement, Recurring [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Trading - other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	427	317
Fair Value Measurement, Recurring [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	16,692	17,186
Available-for-sale securities	11,263,492	11,211,211
Derivative Assets, Fair Value	266,599	281,329
Total	11,546,783	11,509,726
Derivative Liabilities, Fair Value	146,429	136,452
Securities sold not yet purchased	8,290	4,052
Total	154,719	140,504
Fair Value Measurement, Recurring [Member] \| Significant Other Observable Inputs (Level 2) [Member] \| Collateralized loan obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	554,195	534,380
Fair Value Measurement, Recurring [Member] \| U.S. Treasury [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities		2,636
Available-for-sale securities	2,257,713	2,320,815
Fair Value Measurement, Recurring [Member] \| U.S. Treasury [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities		2,636
Available-for-sale securities	2,257,713	2,320,815
Fair Value Measurement, Recurring [Member] \| U.S. Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	5,397	62,370
Available-for-sale securities	49,968	13,489
Fair Value Measurement, Recurring [Member] \| U.S. Agencies [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	5,397	62,370
Available-for-sale securities	49,968	13,489
Fair Value Measurement, Recurring [Member] \| Mortgage-backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	5,172
Available-for-sale securities	8,287,873	8,167,873
Fair Value Measurement, Recurring [Member] \| Mortgage-backed [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	5,172
Available-for-sale securities	8,287,873	8,167,873
Fair Value Measurement, Recurring [Member] \| State and political subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	6,123	3,697
Available-for-sale securities	2,371,456	2,446,588
Fair Value Measurement, Recurring [Member] \| State and political subdivisions [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	6,123	3,697
Available-for-sale securities	2,371,456	2,446,588
Fair Value Measurement, Recurring [Member] \| Corporates [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	7,086	2,192
Available-for-sale securities	139,681	177,115
Fair Value Measurement, Recurring [Member] \| Corporates [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	7,086	2,192
Available-for-sale securities	$ 139,681	$ 177,115

Equity securities with readily determinable fair values.

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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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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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Fair value, after offset of derivative liability, of 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, before offset against an obligation to return collateral under a master netting arrangement. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

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- Definition

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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Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

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Fair value of financial instruments sold short by a broker-dealer for their own account (proprietary securities) for trading or investment purposes determined by management based upon quoted prices of a financial instrument with similar characteristics or on a valuation technique or model.

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Amount of investment in debt security measured at fair value with change in fair value recognized in net income (trading) and investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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