Fair Value Measurements (Estimated Fair Values of Financial Instruments) (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 10,288,853	$ 3,788,181	$ 3,955,779	$ 5,053,047
Securities held to maturity	1,945,833	2,030,005
Loans, net	17,218,132	14,618,165
Deposits	35,015,761	27,639,564
Federal funds purchased and repurchase agreements	2,116,997	1,695,342
Junior subordinated deferrable interest debentures	136,357	136,299
Subordinated notes payable and other borrowings	99,021	98,865
Carrying Amount [Member] \| Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	10,288,853	3,788,181
Securities held to maturity	1,945,673	2,030,005
Cash surrender value of life insurance policies	189,984	187,156
Accrued interest receivable	181,432	183,850
Deposits	35,015,761	27,639,564
Federal funds purchased and repurchase agreements	2,116,997	1,695,342
Junior subordinated deferrable interest debentures	136,357	136,299
Subordinated notes payable and other borrowings	99,021	98,865
Accrued interest payable	8,127	12,393
Carrying Amount [Member] \| Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net	17,218,132	14,618,165
Estimated Fair Value [Member] \| Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	10,288,853	3,788,181
Securities held to maturity	2,052,896	2,048,675
Cash surrender value of life insurance policies	189,984	187,156
Accrued interest receivable	181,432	183,850
Deposits	35,018,185	27,641,255
Federal funds purchased and repurchase agreements	2,116,997	1,695,342
Junior subordinated deferrable interest debentures	137,115	137,115
Subordinated notes payable and other borrowings	115,717	89,077
Accrued interest payable	8,127	12,393
Estimated Fair Value [Member] \| Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net	$ 17,390,683	$ 14,654,615

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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Amount after offset of short term borrowing where a bank borrows, at the federal funds rate, from another bank and securities that an entity sells and agrees to repurchase at a specified date for a specified price.

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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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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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