Fair Value Measurements (Estimated Fair Values of Financial Instruments) (Detail) (USD $)	Dec. 31, 2013	Dec. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 4,556,125,000	$ 3,524,979,000
Securities held to maturity	3,139,748,000	2,956,381,000
Loans, net	9,423,262,000	9,119,395,000
Deposits	20,688,786,000	19,497,366,000
Federal funds purchased and repurchase agreements	668,253,000	561,061,000
Junior subordinated deferrable interest debentures	123,712,000	123,712,000
Subordinated notes payable and other borrowings	100,000,000	100,007,000
Carrying Amount [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	4,556,125,000	3,524,979,000
Securities held to maturity	3,139,748,000	2,956,381,000
Cash surrender value of life insurance policies	141,108,000	138,005,000
Accrued interest receivable	99,281,000	82,529,000
Deposits	20,688,786,000	19,497,366,000
Federal funds purchased and repurchase agreements	668,253,000	561,061,000
Junior subordinated deferrable interest debentures	123,712,000	123,712,000
Subordinated notes payable and other borrowings	100,000,000	100,007,000
Accrued interest payable	1,300,000	1,804,000
Carrying Amount [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net	9,423,262,000	9,119,395,000
Estimated Fair Value [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	4,556,125,000	3,524,979,000
Securities held to maturity	3,029,663,000	2,996,944,000
Cash surrender value of life insurance policies	141,108,000	138,005,000
Accrued interest receivable	99,281,000	82,529,000
Deposits	20,689,323,000	19,498,518,000
Federal funds purchased and repurchase agreements	668,253,000	561,061,000
Junior subordinated deferrable interest debentures	123,712,000	123,712,000
Subordinated notes payable and other borrowings	92,552,000	89,596,000
Accrued interest payable	1,300,000	1,804,000
Estimated Fair Value [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net	$ 9,582,734,000	$ 9,212,159,000