Fair Value Measurements (Summary Of Estimated Fair Values Of Significant Financial Instruments) (Detail) (USD $)	Jun. 30, 2013		Dec. 31, 2012
Fair Value Measurements [Line Items]
Securities available for sale	$ 3,257,360,000		$ 3,136,160,000
Securities held-to-maturity	3,129,864,000
Loans held for sale	81,161,000		107,633,000
Loans and leases, net	12,082,851,000		11,851,567,000
Securities sold under agreements to repurchase and other borrowings	1,213,349,000		1,076,160,000
Federal Home Loan Bank advances	1,627,517,000		1,827,612,000
Long-term debt	229,928,000		334,276,000
Mortgage servicing assets, reserves	500,000		1,800,000
Hedge accounting adjustments and discounts	73,000		85,000
Hedge Accounting Adjustments And Discounts - Long Term Debt	2,700,000		4,400,000
Carrying Balance [Member]
Fair Value Measurements [Line Items]
Securities available for sale	3,257,360,000		3,136,160,000
Securities held-to-maturity	3,129,864,000		3,107,529,000
Loans held for sale	81,161,000		107,633,000
Loans and leases, net	12,082,851,000		11,851,567,000
Mortgage servicing assets	18,764,000	[1]	14,027,000	[1]
Investments in private equity funds	12,587,000		11,623,000
Derivative instruments	37,439,000		50,969,000
Investments held in Rabbi Trust	5,604,000		5,741,000
Deposits other than time deposits	12,494,979,000		11,985,683,000
Time deposits	2,340,596,000		2,545,152,000
Securities sold under agreements to repurchase and other borrowings	1,213,349,000		1,076,160,000
Federal Home Loan Bank advances	1,627,516,000	[2]	1,827,612,000	[2]
Long-term debt	229,928,000	[3]	334,276,000	[3]
Derivative instruments	24,433,000		43,301,000
Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Fair Value Measurements [Line Items]
Securities available for sale	9,091,000		8,282,000
Securities held-to-maturity	0		0
Loans held for sale	0		0
Loans and leases, net	0		0
Mortgage servicing assets	0	[1]	0	[1]
Investments in private equity funds	0		0
Derivative instruments	141,000		0
Investments held in Rabbi Trust	5,604,000		5,741,000
Deposits other than time deposits	0		0
Time deposits	0		0
Securities sold under agreements to repurchase and other borrowings	0		0
Federal Home Loan Bank advances	0	[2]	0	[2]
Long-term debt	0	[3]	0	[3]
Derivative instruments	0		125,000
Significant Other Observable Inputs (Level 2) [Member]
Fair Value Measurements [Line Items]
Securities available for sale	3,218,054,000		3,013,131,000
Securities held-to-maturity	3,174,148,000		3,264,718,000
Loans held for sale	0		0
Loans and leases, net	0		0
Mortgage servicing assets	0	[1]	0	[1]
Investments in private equity funds	0		0
Derivative instruments	37,298,000		50,969,000
Investments held in Rabbi Trust	0		0
Deposits other than time deposits	12,494,979,000		11,985,683,000
Time deposits	2,364,139,000		2,584,921,000
Securities sold under agreements to repurchase and other borrowings	1,247,264,000		1,134,614,000
Federal Home Loan Bank advances	1,636,387,000	[2]	1,843,615,000	[2]
Long-term debt	221,146,000	[3]	298,807,000	[3]
Derivative instruments	24,433,000		43,176,000
Significant Unobservable Input (Level 3) [Member]
Fair Value Measurements [Line Items]
Securities available for sale	30,215,000		114,747,000
Securities held-to-maturity	0		0
Loans held for sale	81,161,000		107,633,000
Loans and leases, net	12,183,704,000		12,005,555,000
Mortgage servicing assets	23,384,000	[1]	15,881,000	[1]
Investments in private equity funds	12,587,000		11,623,000
Derivative instruments	0		0
Investments held in Rabbi Trust	0		0
Deposits other than time deposits	0		0
Time deposits	0		0
Securities sold under agreements to repurchase and other borrowings	0		0
Federal Home Loan Bank advances	0	[2]	0	[2]
Long-term debt	0	[3]	0	[3]
Derivative instruments	$ 0		$ 0

[1] The carrying amount of mortgage servicing assets is net of $0.5 million and $1.8 million reserves at June 30, 2013 and December 31, 2012, respectively. The estimated fair value does not include such adjustments.

[2] The carrying amount of FHLB advances is net of $73 thousand and $85 thousand in unamortized premiums at June 30, 2013 and December 31, 2012, respectively. The estimated fair value does not include such adjustments.

[3] The carrying amount of long-term debt is net of $2.7 million and $4.4 million in hedge accounting adjustments and discounts at June 30, 2013 and December 31, 2012, respectively. The estimated fair value does not include such adjustments.