Fair Value Of Assets And Liabilities (Summary Of Carrying Amounts And Estimated Fair Values Of Financial Instruments) (Detail) (USD $)	Sep. 30, 2012	Jun. 30, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Dec. 31, 2010
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest bearing deposits with banks	$ 934,430,000		$ 749,287,000	$ 1,101,353,000
Available-for-sale securities	1,256,768,000		1,291,797,000	1,267,682,000
Trading account securities	635,000		2,490,000	297,000
Brokerage customer receivables	30,633,000		27,925,000	27,935,000
Mortgage loans held-for-sale, at fair value	548,300,000			204,100,000
Mortgage loans held-for-sale, at lower of cost or market	21,685,000		13,686,000	8,955,000
Total loans	12,147,425,000		11,172,745,000	10,952,786,000
FDIC Indemnification Asset	238,305,000	222,568,000	344,251,000	379,306,000	110,049,000	118,182,000
Notes payable	2,275,000		52,822,000	3,004,000
Federal Home Loan Bank advances	414,211,000		474,481,000	474,570,000
Subordinated notes	15,000,000		35,000,000	40,000,000
Other borrowings	377,229,000		443,753,000	448,082,000
Secured borrowings-owed to securitization investors	0	360,800,000	600,000,000	600,000,000
Junior subordinated debentures	249,493,000		249,493,000	249,493,000
Carrying (Reported) Amount, Fair Value Disclosure [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	212,814,000		169,704,000
Interest bearing deposits with banks	934,430,000		749,287,000
Available-for-sale securities	1,256,768,000		1,291,797,000
Trading account securities	635,000		2,490,000
Brokerage customer receivables	30,633,000		27,925,000
Federal Home Loan Bank and Federal Reserve Bank stock, at cost	80,687,000		100,434,000
Mortgage loans held-for-sale, at fair value	548,300,000		306,838,000
Mortgage loans held-for-sale, at lower of cost or market	21,685,000		13,686,000
Total loans	12,147,425,000		11,172,745,000
Mortgage servicing rights	6,276,000		6,700,000
Nonqualified deferred compensation assets	5,438,000		4,299,000
Derivative assets	65,990,000		38,607,000
FDIC Indemnification Asset	238,305,000		344,251,000
Accrued interest receivable and other	157,923,000		147,207,000
Total financial assets	15,707,309,000		14,375,970,000
Non-maturity deposits	8,736,432,000		7,424,367,000
Deposits with stated maturities	5,111,533,000		4,882,900,000
Notes payable	2,275,000		52,822,000
Federal Home Loan Bank advances	414,211,000		474,481,000
Subordinated notes	15,000,000		35,000,000
Other borrowings	377,229,000		443,753,000
Secured borrowings-owed to securitization investors	0		600,000,000
Junior subordinated debentures	249,493,000		249,493,000
Derivative liabilities	79,977,000		50,081,000
Accrued interest payable and other	11,133,000		12,952,000
Total financial liabilities	14,997,283,000		14,225,849,000
Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	212,814,000		169,704,000
Interest bearing deposits with banks	934,430,000		749,287,000
Available-for-sale securities	1,256,768,000		1,291,797,000
Trading account securities	635,000		2,490,000
Brokerage customer receivables	30,633,000		27,925,000
Federal Home Loan Bank and Federal Reserve Bank stock, at cost	80,687,000		100,434,000
Mortgage loans held-for-sale, at fair value	548,300,000		306,838,000
Mortgage loans held-for-sale, at lower of cost or market	22,042,000		13,897,000
Total loans	12,835,354,000		11,590,729,000
Mortgage servicing rights	6,276,000		6,700,000
Nonqualified deferred compensation assets	5,438,000		4,299,000
Derivative assets	65,990,000		38,607,000
FDIC Indemnification Asset	238,305,000		344,251,000
Accrued interest receivable and other	157,923,000		147,207,000
Total financial assets	16,395,595,000		14,794,165,000
Non-maturity deposits	8,736,432,000		7,424,367,000
Deposits with stated maturities	5,149,824,000		4,917,740,000
Notes payable	2,275,000		52,822,000
Federal Home Loan Bank advances	427,006,000		507,368,000
Subordinated notes	15,000,000		35,000,000
Other borrowings	377,229,000		443,753,000
Secured borrowings-owed to securitization investors	0		603,294,000
Junior subordinated debentures	250,385,000		185,199,000
Derivative liabilities	79,977,000		50,081,000
Accrued interest payable and other	11,133,000		12,952,000
Total financial liabilities	$ 15,049,261,000		$ 14,232,576,000