Fair Value Measurements (Estimated Fair Values of Financial Instruments) (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 4,141,445	$ 3,591,523	$ 4,364,123	$ 4,556,125
Securities held to maturity	2,250,460	2,663,009
Loans, net	11,822,347	11,350,672
Deposits	25,811,575	24,343,595
Federal funds purchased and repurchase agreements	976,992	893,522
Junior subordinated deferrable interest debentures	136,127	136,069
Subordinated notes payable and other borrowings	99,990	99,870
Carrying Amount [Member] \| Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	4,141,445	3,591,523
Securities held to maturity	2,250,460	2,663,009
Cash surrender value of life insurance policies	177,884	175,191
Accrued interest receivable	156,714	139,986
Deposits	25,811,575	24,343,595
Federal funds purchased and repurchase agreements	976,992	893,522
Junior subordinated deferrable interest debentures	136,127	136,069
Subordinated notes payable and other borrowings	99,990	99,870
Accrued interest payable	1,204	1,014
Carrying Amount [Member] \| Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net	11,822,347	11,350,672
Estimated Fair Value [Member] \| Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	4,141,445	3,591,523
Securities held to maturity	2,262,747	2,710,685
Cash surrender value of life insurance policies	177,884	175,191
Accrued interest receivable	156,714	139,986
Deposits	25,812,039	24,344,007
Federal funds purchased and repurchase agreements	976,992	893,522
Junior subordinated deferrable interest debentures	137,115	137,115
Subordinated notes payable and other borrowings	100,000	99,000
Accrued interest payable	1,204	1,014
Estimated Fair Value [Member] \| Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net	$ 11,903,956	$ 11,396,158

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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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 after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

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

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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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