Fair Value Of Assets And Liabilities (Summary Of Carrying Amounts And Estimated Fair Values Of Financial Instruments) (Detail) (USD $)	Sep. 30, 2013	Jun. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Mar. 31, 2012	Dec. 31, 2011
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest bearing deposits with banks	$ 681,834,000		$ 1,035,743,000	$ 934,430,000
Available-for-sale securities	1,781,883,000		1,796,076,000	1,256,768,000
Trading account securities	259,000		583,000	635,000
Brokerage customer receivables	29,253,000		24,864,000	30,633,000
Mortgage loans held-for-sale, at lower of cost or market	5,159,000		27,167,000	21,685,000
FDIC Indemnification asset	100,313,000	137,681,000	208,160,000	238,305,000	222,568,000	344,251,000
Federal Home Loan Bank advances	387,852,000		414,122,000	414,211,000
Subordinated notes	10,000,000		15,000,000	15,000,000
Other borrowings	246,870,000		274,411,000	377,229,000
Junior subordinated debentures	249,493,000		249,493,000	249,493,000
Carrying Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	330,637,000		315,028,000	212,814,000
Interest bearing deposits with banks	681,834,000		1,035,743,000	934,430,000
Available-for-sale securities	1,781,883,000		1,796,076,000	1,256,768,000
Trading account securities	259,000		583,000	635,000
Brokerage customer receivables	29,253,000		24,864,000	30,633,000
Federal Home Loan Bank and Federal Reserve Bank stock, at cost	76,755,000		79,564,000	80,687,000
Mortgage loans held-for-sale, at fair value	329,186,000		385,033,000	548,300,000
Mortgage loans held-for-sale, at lower of cost or market	5,159,000		27,167,000	21,685,000
Total loans	12,997,027,000		12,389,030,000	12,147,425,000
Mortgage servicing rights	8,608,000		6,750,000	6,276,000
Nonqualified deferred compensation assets	6,801,000		5,532,000	5,438,000
Derivative assets	57,573,000		53,906,000	65,990,000
FDIC Indemnification asset	100,313,000		208,160,000	238,305,000
Accrued interest receivable and other	165,209,000		157,157,000	157,923,000
Total financial assets	16,570,497,000		16,484,593,000	15,707,309,000
Non-maturity deposits	10,386,493,000		9,447,633,000	8,736,432,000
Deposits with stated maturities	4,260,953,000		4,980,911,000	5,111,533,000
Notes payable	1,546,000		2,093,000	2,275,000
Federal Home Loan Bank advances	387,852,000		414,122,000	414,211,000
Subordinated notes	10,000,000		15,000,000	15,000,000
Other borrowings	246,870,000		274,411,000	377,229,000
Junior subordinated debentures	249,493,000		249,493,000	249,493,000
Derivative liabilities	49,300,000		57,751,000	79,977,000
Accrued interest payable and other	7,758,000		11,589,000	11,133,000
Total financial liabilities	15,600,265,000		15,453,003,000	14,997,283,000
Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	330,637,000		315,028,000	212,814,000
Interest bearing deposits with banks	681,834,000		1,035,743,000	934,430,000
Available-for-sale securities	1,781,883,000		1,796,076,000	1,256,768,000
Trading account securities	259,000		583,000	635,000
Brokerage customer receivables	29,253,000		24,864,000	30,633,000
Federal Home Loan Bank and Federal Reserve Bank stock, at cost	76,755,000		79,564,000	80,687,000
Mortgage loans held-for-sale, at fair value	329,186,000		385,033,000	548,300,000
Mortgage loans held-for-sale, at lower of cost or market	5,218,000		27,568,000	22,042,000
Total loans	13,576,959,000		13,053,101,000	12,835,354,000
Mortgage servicing rights	8,608,000		6,750,000	6,276,000
Nonqualified deferred compensation assets	6,801,000		5,532,000	5,438,000
Derivative assets	57,573,000		53,906,000	65,990,000
FDIC Indemnification asset	100,313,000		208,160,000	238,305,000
Accrued interest receivable and other	165,209,000		157,157,000	157,923,000
Total financial assets	17,150,488,000		17,149,065,000	16,395,595,000
Non-maturity deposits	10,386,493,000		9,447,633,000	8,736,432,000
Deposits with stated maturities	4,272,459,000		5,013,757,000	5,149,824,000
Notes payable	1,546,000		2,093,000	2,275,000
Federal Home Loan Bank advances	393,602,000		425,431,000	427,006,000
Subordinated notes	10,000,000		15,000,000	15,000,000
Other borrowings	246,870,000		274,411,000	377,229,000
Junior subordinated debentures	250,751,000		250,428,000	250,385,000
Derivative liabilities	49,300,000		57,751,000	79,977,000
Accrued interest payable and other	7,758,000		11,589,000	11,133,000
Total financial liabilities	$ 15,618,779,000		$ 15,498,093,000	$ 15,049,261,000