Disclosures About Fair Value of Financial Instruments - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	$ 35,020	$ 45,618
Securities available for sale	9,299,688	7,447,362
Derivative Assets, Fair Value	103,554	55,276
Derivative Liabilities, Fair Value	9,375	5,997
Securities sold not yet purchased	2,200		$ 14,600
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	14,903	22,216
Securities available for sale	111,939	252,630
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	20,117	23,402
Securities available for sale	9,187,749	7,194,732
U.S. Treasury [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	30,740	64,078
U.S. Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	95,949	93,021
Mortgage-backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	5,468,181	4,071,794
State and political subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	3,623,619	3,029,917
Corporates [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	81,199	188,552
Fair Value Measurement, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	35,020	45,618
Securities available for sale	9,299,688	7,447,362
Equity securities with readily determinable fair values	134,197
Company-owned life insurance	63,575	63,900
Bank-owned life insurance	387,513	280,709
Derivative Assets, Fair Value	103,554	55,276
Total	10,023,547	7,892,865
Derivative Liabilities, Fair Value	9,375	5,997
Securities sold not yet purchased	2,177	14,599
Total	11,552	20,596
Fair Value Measurement, Recurring [Member] \| Trading - other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	13,541	16,567
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	14,903	22,216
Securities available for sale	111,939	252,630
Equity securities with readily determinable fair values	134,197
Total	261,039	274,846
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	13,541	16,567
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	20,117	23,402
Securities available for sale	9,187,749	7,194,732
Company-owned life insurance	63,575	63,900
Bank-owned life insurance	387,513	280,709
Derivative Assets, Fair Value	103,554	55,276
Total	9,762,508	7,618,019
Derivative Liabilities, Fair Value	9,375	5,997
Securities sold not yet purchased	2,177	14,599
Total	11,552	20,596
Fair Value Measurement, Recurring [Member] \| U.S. Treasury [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	651
Securities available for sale	30,740	64,078
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	651
Securities available for sale	30,740	64,078
Fair Value Measurement, Recurring [Member] \| U.S. Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	1,568	1,246
Securities available for sale	95,949	93,021
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	1,568	1,246
Securities available for sale	95,949	93,021
Fair Value Measurement, Recurring [Member] \| Mortgage-backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	4	392
Securities available for sale	5,468,181	4,071,794
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	4	392
Securities available for sale	5,468,181	4,071,794
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	18,545	21,764
Securities available for sale	3,623,619	3,029,917
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	18,545	21,764
Securities available for sale	3,623,619	3,029,917
Fair Value Measurement, Recurring [Member] \| Corporates [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	711	5,649
Securities available for sale	81,199	188,552
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	711	5,649
Securities available for sale	$ 81,199	$ 188,552

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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The carrying amount of a life insurance policy on an officer, executive or employee for which the reporting entity (a bank) is entitled to proceeds from the policy upon death of the insured or surrender of the insurance policy.

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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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Fair value, after offset of derivative asset, of 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, elected not to be and before offset against a right to receive collateral under a master netting arrangement. Includes liabilities elected not to be offset. Excludes liabilities 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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No definition available.

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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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This item represents the amount that could be realized under a life insurance contract or contracts owned by the Entity as of the date of the statement of financial position. Such Entity-owned life insurance policies are commonly known as corporate-owned life insurance (COLI) or bank-owned life insurance (BOLI).

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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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