Fair Value Measurements - Estimated Fair Values of Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013	Dec. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 5,178,131	$ 4,556,125	$ 3,218,460	$ 3,524,979
Securities held to maturity	3,082,082	3,139,748
Loans, net	9,655,489	9,423,262
Deposits	21,065,633	20,688,786
Federal funds purchased and repurchase agreements	515,235	668,253
Junior subordinated deferrable interest debentures	123,712	123,712
Subordinated notes payable and other borrowings	100,000	100,000
Carrying Amount [Member] \| Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	5,178,131	4,556,125
Securities held to maturity	3,082,082	3,139,748
Cash surrender value of life insurance policies	141,790	141,108
Accrued interest receivable	64,998	99,281
Deposits	21,065,633	20,688,786
Federal funds purchased and repurchase agreements	515,235	668,253
Junior subordinated deferrable interest debentures	123,712	123,712
Subordinated notes payable and other borrowings	100,000	100,000
Accrued interest payable	1,176	1,300
Carrying Amount [Member] \| Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net	9,655,489	9,423,262
Estimated Fair Value [Member] \| Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	5,178,131	4,556,125
Securities held to maturity	3,045,459	3,029,663
Cash surrender value of life insurance policies	141,790	141,108
Accrued interest receivable	64,998	99,281
Deposits	21,066,399	20,689,323
Federal funds purchased and repurchase agreements	515,235	668,253
Junior subordinated deferrable interest debentures	123,712	123,712
Subordinated notes payable and other borrowings	93,545	92,552
Accrued interest payable	1,176	1,300
Estimated Fair Value [Member] \| Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net	$ 9,822,107	$ 9,582,734

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

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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 both current and noncurrent portions, carrying amount as of the balance sheet date of other forms of debt not elsewhere specified in the taxonomy with initial maturities beyond one year or beyond the normal operating cycle, if longer.

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