Fair Value Measurements (Summary Of Estimated Fair Values Of Significant Financial Instruments) (Detail) (USD $)	Sep. 30, 2012	Dec. 31, 2011
Fair Value Measurements [Line Items]
Securities available for sale	$ 3,120,354,000	$ 2,874,764,000
Securities held-to-maturity	3,142,160,000	2,973,727,000
Loans held for sale	91,207,000	57,391,000
Loans, net	11,541,563,000	10,991,917,000
Securities sold under agreements to repurchase and other short-term borrowings	1,310,015,000	1,164,706,000
Federal Home Loan Bank advances	1,452,660,000	1,252,609,000
Long-term debt	335,678,000	552,589,000
Mortgage servicing assets, reserves	1,600,000	900,000
Hedge accounting adjustments and discounts	100,000	800,000
Hedge Accounting Adjustments And Discounts - Long Term Debt	5,800,000	11,700,000
Carrying Balance [Member]
Fair Value Measurements [Line Items]
Securities available for sale	3,120,354,000	2,874,764,000
Securities held-to-maturity	3,142,160,000	2,973,727,000
Loans held for sale	91,207,000	57,391,000
Loans, net	11,727,652,000	10,991,917,000
Mortgage servicing assets (a)	12,407,000	7,831,000
Derivative instruments	56,485,000	47,134,000
Investments held in Rabbi Trust	5,706,000
Investments in private equity funds	1,615,000	12,343,000
Deposits other than time deposits	11,786,738,000	10,821,390,000
Time deposits	2,626,699,000	2,834,635,000
Securities sold under agreements to repurchase and other short-term borrowings	1,310,015,000	1,164,706,000
Federal Home Loan Bank advances	1,452,660,000	1,252,609,000
Derivative instruments	64,096,000	59,791,000
Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Fair Value Measurements [Line Items]
Securities available for sale	8,295,000	8,672,000
Securities held-to-maturity	0	0
Loans held for sale	0	0
Loans, net	0	0
Mortgage servicing assets (a)	0	0
Derivative instruments	0	0
Investments held in Rabbi Trust	5,706,000
Investments in private equity funds	0	0
Deposits other than time deposits	0	0
Time deposits	0	0
Securities sold under agreements to repurchase and other short-term borrowings	0	0
Federal Home Loan Bank advances	0	0
Long-term debt	0	0
Derivative instruments	447,000	0
Significant Other Observable Inputs (Level 2) [Member]
Fair Value Measurements [Line Items]
Securities available for sale	3,083,806,000	2,836,119,000
Securities held-to-maturity	3,321,317,000	3,130,546,000
Loans held for sale	0	0
Loans, net	0	0
Mortgage servicing assets (a)	0	0
Derivative instruments	56,485,000	47,134,000
Investments held in Rabbi Trust	0
Investments in private equity funds	0	0
Deposits other than time deposits	11,786,738,000	10,619,712,000
Time deposits	2,670,366,000	2,883,006,000
Securities sold under agreements to repurchase and other short-term borrowings	1,373,475,000	1,212,228,000
Federal Home Loan Bank advances	1,478,212,000	1,283,871,000
Long-term debt	296,667,000	505,635,000
Derivative instruments	63,649,000	59,791,000
Significant Unobservable Input (Level 3) [Member]
Fair Value Measurements [Line Items]
Securities available for sale	28,253,000	29,973,000
Securities held-to-maturity	0	0
Loans held for sale	91,207,000	57,391,000
Loans, net	11,626,902,000	11,097,390,000
Mortgage servicing assets (a)	12,811,000	9,968,000
Derivative instruments	0	0
Investments held in Rabbi Trust	0
Investments in private equity funds	1,615,000	12,343,000
Deposits other than time deposits	0	0
Time deposits	0	0
Securities sold under agreements to repurchase and other short-term borrowings	0	0
Federal Home Loan Bank advances	0	0
Long-term debt	0	0
Derivative instruments	$ 0	$ 0