Fair Value Measurements - Estimated Fair Values of Financial Instruments (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 16,253,971	$ 10,288,853	$ 7,175,680	$ 3,788,181
Securities held to maturity	1,759,428	1,945,833
Loans, net	15,582,520	17,218,132
Deposits	39,612,767	35,015,761
Federal funds purchased	27,200	48,850
Repurchase agreements	2,200,029	2,068,147
Junior subordinated deferrable interest debentures, net of unamortized issuance costs	136,400	136,357
Subordinated notes	99,139	99,021
Carrying Amount [Member] \| Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	16,253,971	10,288,853
Securities held to maturity	1,759,270	1,945,673
Cash surrender value of life insurance policies	189,941	189,984
Accrued interest receivable	119,232	181,432
Deposits	39,612,767	35,015,761
Federal funds purchased	27,200	48,850
Repurchase agreements	2,200,029	2,068,147
Junior subordinated deferrable interest debentures, net of unamortized issuance costs	136,400	136,357
Subordinated notes	99,139	99,021
Accrued interest payable	2,126	8,127
Carrying Amount [Member] \| Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net	15,582,520	17,218,132
Estimated Fair Value [Member] \| Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	16,253,971	10,288,853
Securities held to maturity	1,825,568	2,052,896
Cash surrender value of life insurance policies	189,941	189,984
Accrued interest receivable	119,232	181,432
Deposits	39,613,343	35,018,185
Federal funds purchased	27,200	48,850
Repurchase agreements	2,200,029	2,068,147
Junior subordinated deferrable interest debentures, net of unamortized issuance costs	137,115	137,115
Subordinated notes	113,223	115,717
Accrued interest payable	2,126	8,127
Estimated Fair Value [Member] \| Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net	$ 15,656,269	$ 17,390,683

The sum of cash and cash equivalents plus Federal Funds Sold. Cash and cash equivalents consist of short term, highly liquid investments that are readily convertible to known amounts of cash and are so near their maturity that they present negligible risk of changes in value due to changes in interest rates -- usually with an original maturity less than 90 days.

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Carrying amount as of the balance sheet date of amounts which could be received based on the terms of the insurance contract upon surrendering life policies owned by the entity.

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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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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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Amount of short term borrowing where a bank borrows, at the federal funds rate, from another bank.

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

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Amount of interest payable on debt, including, but not limited to, trade payables.

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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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Including the current and noncurrent portions, carrying value as of the balance sheet date of long-term debt (with maturities initially due after one year or beyond the operating cycle if longer) identified as Junior Subordinated Notes, which have a lower priority than senior instruments.

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Amount after allowance and deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements and loans held for sale.

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Amount, after the effects of master netting arrangements, of funds outstanding borrowed in the form of a security repurchase agreement between the entity and another party for the sale and repurchase of identical or substantially the same securities at a date certain for a specified price. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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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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