Fair Value Measurements, Financial Instruments (Details) (USD $)	Jun. 30, 2013		Mar. 31, 2013	Dec. 31, 2012		Jun. 30, 2012		Mar. 31, 2012	Dec. 31, 2011
Investment securities [Abstract]
Total investment securities	$ 615,790,000	[1]		$ 499,534,000	[2]	$ 412,479,000	[3]
Fair Value Option Securities [Abstract]
Residential mortgage loans held for sale	301,057,000			293,762,000		259,174,000
Loans [Abstract]
Total	12,440,782,000			12,311,456,000		11,576,431,000
Allowance for loan losses	(203,124,000)		(205,965,000)	(215,507,000)		(231,669,000)		(244,209,000)	(253,481,000)
Loans, net of allowance	12,237,658,000			12,095,949,000		11,344,762,000
Mortgage servicing rights, Fair Value Disclosure	132,889,000		109,840,000	100,812,000		91,783,000		98,138,000	86,783,000
Derviative contracts, net of cash margin, assets, Fair Value Disclosure	546,206,000			338,106,000		366,204,000
Time deposits	2,767,972,000			2,967,992,000		3,107,950,000
Subordinated debentures	347,716,000			347,633,000		353,378,000
Derivative contracts net of cash margin, liabilities, Fair Value DIsclosure	521,991,000			283,589,000		370,053,000
Fair Value Assumptions and Methodology for Assets and Liabilities [Abstract]
Specific allocation of allowance for loan losses included in fair value of loans	161,000,000			171,000,000		191,000,000
Carrying (Reported) Amount, Fair Value Disclosure [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	1,078,385,000			1,286,239,000		639,263,000
Trading Securities [Abstract]
U.S. Government Agency Debentures, Trading Securities, Fair Value Disclosure	60,713,000			16,545,000		53,514,000
U.S. Agency Residential Mortgage-backed Securities, Trading Securities, Fair Value Disclosure	43,858,000			86,361,000		46,502,000
Municipal And Other-tax Exempt Securities, Trading Securities, Fair Value Disclosure	53,819,000			90,326,000		44,632,000
Other Trading Securities, Trading Securities, Fair Value Disclosure	32,201,000			20,870,000		4,669,000
Trading Securities, Fair Value Disclosure	190,591,000			214,102,000		149,317,000
Investment securities [Abstract]
Municipal and other tax-exempt	375,317,000			232,700,000		126,168,000
U.S. agency residential mortgage-backed securities	64,172,000			82,767,000		102,347,000
Other debt securities	176,301,000			184,067,000		183,964,000
Total investment securities	615,790,000			499,534,000		412,479,000
Available for sale securities [Abstract]
U.S. Treasury Securities, Available for Sale Securities, Fair Value DIsclosure	1,060,000			1,002,000		1,003,000
Municipal and Other Tax-exempt Securities, Available for Sale Securities, Fair Value Disclosure	95,103,000			87,142,000		88,458,000
U.S. Agency Residential Mortgage-backed Securities. Available for Sale Securities, Fair Value Disclosure	8,372,795,000			9,889,821,000		9,903,532,000
Privately Issued Residential Mortgage-backed Securities, Available for Sale Securities, Fair Value Disclosure	297,175,000			325,163,000		317,761,000
Commercial Mortgage-backed Securities, Available for Sale Securities, Fair Value Disclosure	1,846,943,000			895,075,000
Other Debt Securities, Available for Sale Securities, Fair Value Disclosure	35,894,000			36,389,000		36,286,000
Perpetual Preferred Stock, Available for Sale Securities, Fair Value Disclosure	25,583,000			25,072,000		23,431,000
Equity Securities and Mutual Funds, Available for Sale Securities, Fair Value Disclosure	23,521,000			27,557,000		24,944,000
Available for Sale Securities, Fair Value Disclosure	10,698,074,000			11,287,221,000		10,395,415,000
Fair Value Option Securities [Abstract]
U.S. Agency Residential Mortgage-backed Securities, Fair Value Option Securities, Fair Value Disclosure	203,816,000			257,040,000		299,467,000
Corporate Debt Securities, Fair Value Option Securities, Fair Value Disclosure				26,486,000		25,710,000
Other Securities, Fair Value Option Securities, Fair Value Disclosure	1,940,000			770,000
Fair Value Option Securities, Fair Value Disclosure	205,756,000			284,296,000		325,177,000
Residential mortgage loans held for sale	301,057,000			293,762,000		259,174,000
Loans [Abstract]
Commercial	7,708,120,000			7,641,912,000		7,035,535,000
Commercial real estate	2,317,096,000			2,228,999,000		2,149,730,000
Residential mortgage	2,039,785,000			2,045,040,000		2,002,885,000
Consumer	375,781,000			395,505,000		388,281,000
Total	12,440,782,000			12,311,456,000		11,576,431,000
Allowance for loan losses	(203,124,000)			(215,507,000)		(231,669,000)
Loans, net of allowance	12,237,658,000			12,095,949,000		11,344,762,000
Mortgage servicing rights, Fair Value Disclosure	132,889,000			100,812,000		91,783,000
Derviative contracts, net of cash margin, assets, Fair Value Disclosure	546,206,000			338,106,000		366,204,000
Other assets - private equity funds	28,379,000			28,169,000		31,492,000
Deposits with no stated maturity	16,728,258,000			18,211,068,000		15,157,587,000
Time deposits	2,767,972,000			2,967,992,000		3,107,950,000
Other borrowings	4,073,915,000			2,706,221,000		2,648,753,000
Subordinated debentures	347,716,000			347,633,000		353,378,000
Derivative contracts net of cash margin, liabilities, Fair Value DIsclosure	521,991,000			283,589,000		370,053,000
Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	1,078,385,000			1,286,239,000		639,263,000
Trading Securities [Abstract]
U.S. Government Agency Debentures, Trading Securities, Fair Value Disclosure	60,713,000			16,545,000		53,514,000
U.S. Agency Residential Mortgage-backed Securities, Trading Securities, Fair Value Disclosure	43,858,000			86,361,000		46,502,000
Municipal And Other-tax Exempt Securities, Trading Securities, Fair Value Disclosure	53,819,000			90,326,000		44,632,000
Other Trading Securities, Trading Securities, Fair Value Disclosure	32,201,000			20,870,000		4,669,000
Trading Securities, Fair Value Disclosure	190,591,000			214,102,000		149,317,000
Investment securities [Abstract]
Municipal and other tax-exempt	371,690,000			235,940,000		130,308,000
U.S. agency residential mortgage-backed securities	66,796,000			85,943,000		105,535,000
Other debt securities	187,219,000			206,575,000		204,795,000
Total investment securities	625,705,000			528,458,000		440,638,000
Available for sale securities [Abstract]
U.S. Treasury Securities, Available for Sale Securities, Fair Value DIsclosure	1,060,000			1,002,000		1,003,000
Municipal and Other Tax-exempt Securities, Available for Sale Securities, Fair Value Disclosure	95,103,000			87,142,000		88,458,000
U.S. Agency Residential Mortgage-backed Securities. Available for Sale Securities, Fair Value Disclosure	8,372,795,000			9,889,821,000		9,903,532,000
Privately Issued Residential Mortgage-backed Securities, Available for Sale Securities, Fair Value Disclosure	297,175,000			325,163,000		317,761,000
Commercial Mortgage-backed Securities, Available for Sale Securities, Fair Value Disclosure	1,846,943,000			895,075,000
Other Debt Securities, Available for Sale Securities, Fair Value Disclosure	35,894,000			36,389,000		36,286,000
Perpetual Preferred Stock, Available for Sale Securities, Fair Value Disclosure	25,583,000			25,072,000		23,431,000
Equity Securities and Mutual Funds, Available for Sale Securities, Fair Value Disclosure	23,521,000			27,557,000		24,944,000
Available for Sale Securities, Fair Value Disclosure	10,698,074,000			11,287,221,000		10,395,415,000
Fair Value Option Securities [Abstract]
U.S. Agency Residential Mortgage-backed Securities, Fair Value Option Securities, Fair Value Disclosure	203,816,000			257,040,000		299,467,000
Corporate Debt Securities, Fair Value Option Securities, Fair Value Disclosure				26,486,000		25,710,000
Other Securities, Fair Value Option Securities, Fair Value Disclosure	1,940,000			770,000
Fair Value Option Securities, Fair Value Disclosure	205,756,000			284,296,000		325,177,000
Residential mortgage loans held for sale	301,057,000			293,762,000		259,174,000
Loans [Abstract]
Commercial	7,638,327,000			7,606,505,000		6,993,377,000
Commercial real estate	2,288,188,000			2,208,217,000		2,129,731,000
Residential mortgage	2,038,375,000			2,110,773,000		2,040,062,000
Consumer	369,375,000			388,748,000		383,088,000
Total	12,334,265,000			12,314,243,000		11,546,258,000
Allowance for loan losses	0			0		0
Loans, net of allowance	12,334,265,000			12,314,243,000		11,546,258,000
Mortgage servicing rights, Fair Value Disclosure	132,889,000			100,812,000		91,783,000
Derviative contracts, net of cash margin, assets, Fair Value Disclosure	546,206,000			338,106,000		366,204,000
Other assets - private equity funds	28,379,000			28,169,000		31,492,000
Deposits with no stated maturity	16,728,258,000			18,211,068,000		15,157,587,000
Time deposits	2,781,202,000			3,037,708,000		3,175,687,000
Other borrowings	4,034,685,000			2,696,574,000		2,642,598,000
Subordinated debentures	345,201,000			345,675,000		350,813,000
Derivative contracts net of cash margin, liabilities, Fair Value DIsclosure	521,991,000			283,589,000		370,053,000
Contractual Yield, Minimum [Member]
Loans [Abstract]
Commercial	0.0025			0.0021		0.0025
Commercial real estate	0.0038			0.0021		0.0038
Residential mortgage	0.0038			0.0038		0.0038
Consumer	0.0038			0.0038		0.0038
Time deposits	0.0003			0.0001		0.0001
Other borrowings	0.0025			0.0009		0.0009
Subordinated debentures	0.0097			0.0100		0.0116
Contractual Yield, Maximum [Member]
Loans [Abstract]
Commercial	0.3000			0.3000		0.3000
Commercial real estate	0.1800			0.1800		0.1800
Residential mortgage	0.1800			0.1800		0.1800
Consumer	0.2100			0.2100		0.2100
Time deposits	0.0964			0.0964		0.0964
Other borrowings	0.0525			0.0525		0.0525
Subordinated debentures	0.0500			0.0500		0.0500
Average Repricing [Member]
Loans [Abstract]
Commercial	0.63			0.69		0.70
Commercial real estate	0.83			0.92		0.92
Residential mortgage	3.64			3.34		3.10
Consumer	0.35			0.32		0.34
Time deposits	2.02			2.15		2.17
Other borrowings	0.00			0.00		0.00
Subordinated debentures	3.10			3.56		4.02
Discount Rate, Minimum [Member]
Loans [Abstract]
Commercial	0.0059			0.0051		0.0063
Commercial real estate	0.0123			0.0126		0.0133
Residential mortgage	0.0070			0.0086		0.0108
Consumer	0.0126			0.0137		0.0159
Time deposits	0.0076			0.0080		0.0092
Other borrowings	0.0007			0.0009		0.0009
Subordinated debentures	0.0224			0.0240		0.0240
Discount Rate, Maximum [Member]
Loans [Abstract]
Commercial	0.0419			0.0359		0.0368
Commercial real estate	0.0347			0.0318		0.0333
Residential mortgage	0.0446			0.0309		0.0352
Consumer	0.0374			0.0360		0.0379
Time deposits	0.0130			0.0115		0.0131
Other borrowings	0.0266			0.0267		0.0270
Subordinated debentures	$ 0.0224			$ 0.0240		$ 0.0240

[1] Carrying value includes $3.0 million of net unrealized gain which remains in Accumulated other comprehensive income (“AOCI”) related to certain securities transferred from the Available for Sale securities portfolio to the Investment securities portfolio as discussed in greater detail following.

[2] Carrying value includes $5.0 million of net unrealized gain which remains in Accumulated other comprehensive income (“AOCI”) in the Consolidated Balance Sheets related to certain securities transferred from the Available for Sale securities portfolio to the Investment securities portfolio as discussed in greater detail following.

[3] Carrying value includes $8.2 million of net unrealized gain which remains in Accumulated other comprehensive income (“AOCI”) in the Consolidated Balance Sheets related to certain securities transferred from the Available for Sale securities portfolio to the Investment securities portfolio as discussed in greater detail following.