Fair Value Measurements, Financial Instruments (Details) (USD $)	Mar. 31, 2013		Dec. 31, 2012		Mar. 31, 2012		Dec. 31, 2011
Investment securities [Abstract]
Total investment securities	$ 589,271,000	[1]	$ 499,534,000	[2]	$ 427,259,000	[3]
Fair Value Option Securities [Abstract]
Residential mortgage loans held for sale	286,211,000		293,762,000		247,039,000
Loans [Abstract]
Total	12,093,564,000		12,311,456,000		11,577,444,000
Allowance for loan losses	(205,965,000)		(215,507,000)		(244,209,000)		(253,481,000)
Loans, net of allowance	11,887,599,000		12,095,949,000		11,333,235,000
Mortgage servicing rights, Fair Value Disclosure	109,840,000		100,812,000		98,138,000		86,783,000
Derviative contracts, net of cash margin, assets, Fair Value Disclosure	320,473,000		338,106,000		384,996,000
Time deposits	2,900,054,000		2,967,992,000		3,166,099,000
Subordinated debentures	347,674,000		347,633,000		394,760,000
Derivative contracts net of cash margin, liabilities, Fair Value DIsclosure	251,836,000		283,589,000		305,290,000
Fair Value Assumptions and Methodology for Assets and Liabilities [Abstract]
Specific allocation of allowance for loan losses included in fair value of loans	163,000,000		171,000,000		200,000,000
Carrying (Reported) Amount, Fair Value Disclosure [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	945,617,000		1,286,239,000		706,306,000
Trading Securities [Abstract]
U.S. Agency Government Obligations, Trading Securities, Fair Value Disclosure	55,358,000		16,545,000		27,430,000
U.S. Agency Residential Mortgage-backed Securities, Trading Securities, Fair Value Disclosure	33,106,000		86,361,000		35,111,000
Municipal And Other-tax Exempt Securities, Trading Securities, Fair Value Disclosure	90,710,000		90,326,000		60,230,000
Other Trading Securities, Trading Securities, Fair Value Disclosure	27,424,000		20,870,000		5,605,000
Trading Securities, Fair Value Disclosure	206,598,000		214,102,000		128,376,000
Investment securities [Abstract]
Municipal and other tax-exempt	339,003,000		232,700,000		130,919,000
U.S. agency residential mortgage-backed securities	72,968,000		82,767,000		112,909,000
Other debt securities	177,300,000		184,067,000		183,431,000
Total investment securities	589,271,000		499,534,000		427,259,000
Available for sale securities [Abstract]
U.S. Treasury Securities, Available for Sale Securities, Fair Value DIsclosure	1,000,000		1,002,000		1,004,000
Municipal and Other Tax-exempt Securities, Available for Sale Securities, Fair Value Disclosure	85,447,000		87,142,000		72,234,000
U.S. Agency Residential Mortgage-backed Securities. Available for Sale Securities, Fair Value Disclosure	9,165,212,000		9,889,821,000		9,677,602,000
Privately Issued Residential Mortgage-backed Securities, Available for Sale Securities, Fair Value Disclosure	316,208,000		325,163,000		326,513,000
Commercial Mortgage-backed Securities, Available for Sale Securities, Fair Value Disclosure	1,405,346,000		895,075,000
Other Debt Securities, Available for Sale Securities, Fair Value Disclosure	36,079,000		36,389,000		36,777,000
Perpetual Preferred Stock, Available for Sale Securities, Fair Value Disclosure	26,832,000		25,072,000		21,024,000
Equity Securities and Mutual Funds, Available for Sale Securities, Fair Value Disclosure	23,021,000		27,557,000		51,443,000
Available for Sale Securities, Fair Value Disclosure	11,059,145,000		11,287,221,000		10,186,597,000
Fair Value Option Securities [Abstract]
U.S. Agency Residential Mortgage-backed Securities, Fair Value Option Securities, Fair Value Disclosure	208,900,000		257,040,000		322,180,000
Corporate Debt Securities, Fair Value Option Securities, Fair Value Disclosure			26,486,000		25,772,000
Other Securities, Fair Value Option Securities, Fair Value Disclosure	1,292,000		770,000
Fair Value Option Securities, Fair Value Disclosure	210,192,000		284,296,000		347,952,000
Residential mortgage loans held for sale	286,211,000		293,762,000		247,039,000
Loans [Abstract]
Commercial	7,418,305,000		7,641,912,000		6,943,585,000
Commercial real estate	2,285,160,000		2,228,999,000		2,252,299,000
Residential mortgage	2,012,450,000		2,045,040,000		1,968,926,000
Consumer	377,649,000		395,505,000		412,634,000
Total	12,093,564,000		12,311,456,000		11,577,444,000
Allowance for loan losses	(205,965,000)		(215,507,000)		(244,209,000)
Loans, net of allowance	11,887,599,000		12,095,949,000		11,333,235,000
Mortgage servicing rights, Fair Value Disclosure	109,840,000		100,812,000		98,138,000
Derviative contracts, net of cash margin, assets, Fair Value Disclosure	320,473,000		338,106,000		384,996,000
Other assets - private equity funds	29,216,000		28,169,000		30,993,000
Deposits with no stated maturity	16,960,237,000		18,211,068,000		15,357,188,000
Time deposits	2,900,054,000		2,967,992,000		3,166,099,000
Other borrowings	3,393,416,000		2,706,221,000		3,156,717,000
Subordinated debentures	347,674,000		347,633,000		394,760,000
Derivative contracts net of cash margin, liabilities, Fair Value DIsclosure	251,836,000		283,589,000		305,290,000
Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	945,617,000		1,286,239,000		706,306,000
Trading Securities [Abstract]
U.S. Agency Government Obligations, Trading Securities, Fair Value Disclosure	55,358,000		16,545,000		27,430,000
U.S. Agency Residential Mortgage-backed Securities, Trading Securities, Fair Value Disclosure	33,106,000		86,361,000		35,111,000
Municipal And Other-tax Exempt Securities, Trading Securities, Fair Value Disclosure	90,710,000		90,326,000		60,230,000
Other Trading Securities, Trading Securities, Fair Value Disclosure	27,424,000		20,870,000		5,605,000
Trading Securities, Fair Value Disclosure	206,598,000		214,102,000		128,376,000
Investment securities [Abstract]
Municipal and other tax-exempt	341,940,000		235,940,000		135,314,000
U.S. agency residential mortgage-backed securities	76,851,000		85,943,000		113,958,000
Other debt securities	196,403,000		206,575,000		202,171,000
Total investment securities	615,194,000		528,458,000		451,443,000
Available for sale securities [Abstract]
U.S. Treasury Securities, Available for Sale Securities, Fair Value DIsclosure	1,000,000		1,002,000		1,004,000
Municipal and Other Tax-exempt Securities, Available for Sale Securities, Fair Value Disclosure	85,447,000		87,142,000		72,234,000
U.S. Agency Residential Mortgage-backed Securities. Available for Sale Securities, Fair Value Disclosure	9,165,212,000		9,889,821,000		9,677,602,000
Privately Issued Residential Mortgage-backed Securities, Available for Sale Securities, Fair Value Disclosure	316,208,000		325,163,000		326,513,000
Commercial Mortgage-backed Securities, Available for Sale Securities, Fair Value Disclosure	1,405,346,000		895,075,000
Other Debt Securities, Available for Sale Securities, Fair Value Disclosure	36,079,000		36,389,000		36,777,000
Perpetual Preferred Stock, Available for Sale Securities, Fair Value Disclosure	26,832,000		25,072,000		21,024,000
Equity Securities and Mutual Funds, Available for Sale Securities, Fair Value Disclosure	23,021,000		27,557,000		51,443,000
Available for Sale Securities, Fair Value Disclosure	11,059,145,000		11,287,221,000		10,186,597,000
Fair Value Option Securities [Abstract]
U.S. Agency Residential Mortgage-backed Securities, Fair Value Option Securities, Fair Value Disclosure	208,900,000		257,040,000		322,180,000
Corporate Debt Securities, Fair Value Option Securities, Fair Value Disclosure			26,486,000		25,772,000
Other Securities, Fair Value Option Securities, Fair Value Disclosure	1,292,000		770,000
Fair Value Option Securities, Fair Value Disclosure	210,192,000		284,296,000		347,952,000
Residential mortgage loans held for sale	286,211,000		293,762,000		247,039,000
Loans [Abstract]
Commercial	7,372,375,000		7,606,505,000		6,879,803,000
Commercial real estate	2,266,433,000		2,208,217,000		2,254,289,000
Residential mortgage	2,062,801,000		2,110,773,000		2,002,946,000
Consumer	371,771,000		388,748,000		398,149,000
Total	12,073,380,000		12,314,243,000		11,535,187,000
Allowance for loan losses	0		0		0
Loans, net of allowance	12,073,380,000		12,314,243,000		11,535,187,000
Mortgage servicing rights, Fair Value Disclosure	109,840,000		100,812,000		98,138,000
Derviative contracts, net of cash margin, assets, Fair Value Disclosure	320,473,000		338,106,000		384,996,000
Other assets - private equity funds	29,216,000		28,169,000		30,993,000
Deposits with no stated maturity	16,960,237,000		18,211,068,000		15,357,188,000
Time deposits	2,958,570,000		3,037,708,000		3,221,842,000
Other borrowings	3,398,902,000		2,696,574,000		3,153,280,000
Subordinated debentures	345,527,000		345,675,000		405,589,000
Derivative contracts net of cash margin, liabilities, Fair Value DIsclosure	251,836,000		283,589,000		305,290,000
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	0.0013		0.0009		0.0025
Subordinated debentures	0.0098		0.0100		0.0519
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		0.0582
Average Repricing [Member]
Loans [Abstract]
Commercial	0.66		0.69		0.52
Commercial real estate	0.84		0.92		1.30
Residential mortgage	3.53		3.34		3.52
Consumer	0.31		0.32		0.38
Time deposits	2.14		2.15		2.24
Other borrowings	0.00		0.00		0.00
Subordinated debentures	3.33		3.56		1.22
Discount Rate, Minimum [Member]
Loans [Abstract]
Commercial	0.0055		0.0051		0.0058
Commercial real estate	0.0119		0.0126		0.0029
Residential mortgage	0.0074		0.0086		0.0106
Consumer	0.0128		0.0137		0.0173
Time deposits	0.0078		0.0080		0.0094
Other borrowings	0.0013		0.0009		0.0009
Discount Rate, Maximum [Member]
Loans [Abstract]
Commercial	0.0369		0.0359		0.0392
Commercial real estate	0.0321		0.0318		0.0345
Residential mortgage	0.0329		0.0309		0.0386
Consumer	0.0353		0.0360		0.0378
Time deposits	0.0115		0.0115		0.0144
Other borrowings	0.0267		0.0267		0.0270
Subordinated debentures	0.0222		0.0240		0.0299
Fair Value, Measurements, Recurring [Member]
Trading Securities [Abstract]
U.S. Agency Government Obligations, Trading Securities, Fair Value Disclosure	55,358,000		16,545,000		27,430,000
U.S. Agency Residential Mortgage-backed Securities, Trading Securities, Fair Value Disclosure	33,106,000		86,361,000		35,111,000
Municipal And Other-tax Exempt Securities, Trading Securities, Fair Value Disclosure	90,710,000		90,326,000		60,230,000
Other Trading Securities, Trading Securities, Fair Value Disclosure	27,424,000		20,870,000		5,605,000
Trading Securities, Fair Value Disclosure	206,598,000		214,102,000		128,376,000
Available for sale securities [Abstract]
U.S. Treasury Securities, Available for Sale Securities, Fair Value DIsclosure	1,000,000		1,002,000		1,004,000
Municipal and Other Tax-exempt Securities, Available for Sale Securities, Fair Value Disclosure	85,447,000		87,142,000		72,234,000
U.S. Agency Residential Mortgage-backed Securities. Available for Sale Securities, Fair Value Disclosure	9,165,212,000		9,889,821,000		9,677,602,000
Privately Issued Residential Mortgage-backed Securities, Available for Sale Securities, Fair Value Disclosure	316,208,000		325,163,000		326,513,000
Commercial Mortgage-backed Securities, Available for Sale Securities, Fair Value Disclosure	1,405,346,000		895,075,000
Other Debt Securities, Available for Sale Securities, Fair Value Disclosure	36,079,000		36,389,000		36,777,000
Perpetual Preferred Stock, Available for Sale Securities, Fair Value Disclosure	26,832,000		25,072,000		21,024,000
Equity Securities and Mutual Funds, Available for Sale Securities, Fair Value Disclosure	23,021,000		27,557,000		51,443,000
Available for Sale Securities, Fair Value Disclosure	11,059,145,000		11,287,221,000		10,186,597,000
Fair Value Option Securities [Abstract]
U.S. Agency Residential Mortgage-backed Securities, Fair Value Option Securities, Fair Value Disclosure	208,900,000		257,040,000		322,180,000
Corporate Debt Securities, Fair Value Option Securities, Fair Value Disclosure			26,486,000		25,772,000
Other Securities, Fair Value Option Securities, Fair Value Disclosure	1,292,000		770,000
Fair Value Option Securities, Fair Value Disclosure	210,192,000		284,296,000		347,952,000
Loans [Abstract]
Mortgage servicing rights, Fair Value Disclosure	109,840,000	[4]	100,812,000	[4]	98,138,000	[4]
Derviative contracts, net of cash margin, assets, Fair Value Disclosure	320,473,000	[5]	338,106,000	[5]	384,996,000	[5]
Other assets - private equity funds, Fair Value Disclosure	29,216,000		28,169,000		30,993,000
Derivative contracts net of cash margin, liabilities, Fair Value DIsclosure	251,836,000	[5]	283,589,000	[5]	305,290,000	[5]
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Trading Securities [Abstract]
U.S. Agency Government Obligations, Trading Securities, Fair Value Disclosure	0		0		0
U.S. Agency Residential Mortgage-backed Securities, Trading Securities, Fair Value Disclosure	0		0		0
Municipal And Other-tax Exempt Securities, Trading Securities, Fair Value Disclosure	0		0		0
Other Trading Securities, Trading Securities, Fair Value Disclosure	0		0		0
Trading Securities, Fair Value Disclosure	0		0		0
Available for sale securities [Abstract]
U.S. Treasury Securities, Available for Sale Securities, Fair Value DIsclosure	1,000,000		1,002,000		1,004,000
Municipal and Other Tax-exempt Securities, Available for Sale Securities, Fair Value Disclosure	0		0		0
U.S. Agency Residential Mortgage-backed Securities. Available for Sale Securities, Fair Value Disclosure	0		0		0
Privately Issued Residential Mortgage-backed Securities, Available for Sale Securities, Fair Value Disclosure	0		0		0
Commercial Mortgage-backed Securities, Available for Sale Securities, Fair Value Disclosure	0		0
Other Debt Securities, Available for Sale Securities, Fair Value Disclosure	0		0		0
Perpetual Preferred Stock, Available for Sale Securities, Fair Value Disclosure	0		0		0
Equity Securities and Mutual Funds, Available for Sale Securities, Fair Value Disclosure	4,571,000		4,165,000		25,278,000
Available for Sale Securities, Fair Value Disclosure	5,571,000		5,167,000		26,282,000
Fair Value Option Securities [Abstract]
U.S. Agency Residential Mortgage-backed Securities, Fair Value Option Securities, Fair Value Disclosure	0		0		0
Corporate Debt Securities, Fair Value Option Securities, Fair Value Disclosure			0		0
Other Securities, Fair Value Option Securities, Fair Value Disclosure	0		0
Fair Value Option Securities, Fair Value Disclosure	0		0		0
Loans [Abstract]
Mortgage servicing rights, Fair Value Disclosure	0	[4]	0	[4]	0	[4]
Derviative contracts, net of cash margin, assets, Fair Value Disclosure	457,000	[5],[6]	11,597,000	[5],[7]	0	[5],[8]
Other assets - private equity funds, Fair Value Disclosure	0		0		0
Derivative contracts net of cash margin, liabilities, Fair Value DIsclosure	0	[5],[6]	0	[5],[7]	0	[5],[8]
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Trading Securities [Abstract]
U.S. Agency Government Obligations, Trading Securities, Fair Value Disclosure	55,358,000		16,545,000		27,430,000
U.S. Agency Residential Mortgage-backed Securities, Trading Securities, Fair Value Disclosure	33,106,000		86,361,000		35,111,000
Municipal And Other-tax Exempt Securities, Trading Securities, Fair Value Disclosure	90,710,000		90,326,000		60,230,000
Other Trading Securities, Trading Securities, Fair Value Disclosure	27,424,000		20,870,000		5,481,000
Trading Securities, Fair Value Disclosure	206,598,000		214,102,000		128,252,000
Available for sale securities [Abstract]
U.S. Treasury Securities, Available for Sale Securities, Fair Value DIsclosure	0		0		0
Municipal and Other Tax-exempt Securities, Available for Sale Securities, Fair Value Disclosure	46,440,000		46,440,000		30,257,000
U.S. Agency Residential Mortgage-backed Securities. Available for Sale Securities, Fair Value Disclosure	9,165,212,000		9,889,821,000		9,677,602,000
Privately Issued Residential Mortgage-backed Securities, Available for Sale Securities, Fair Value Disclosure	316,208,000		325,163,000		326,513,000
Commercial Mortgage-backed Securities, Available for Sale Securities, Fair Value Disclosure	1,405,346,000		895,075,000
Other Debt Securities, Available for Sale Securities, Fair Value Disclosure	30,886,000		30,990,000		30,877,000
Perpetual Preferred Stock, Available for Sale Securities, Fair Value Disclosure	26,832,000		25,072,000		21,024,000
Equity Securities and Mutual Funds, Available for Sale Securities, Fair Value Disclosure	15,978,000		21,231,000		26,165,000
Available for Sale Securities, Fair Value Disclosure	11,006,902,000		11,233,792,000		10,112,438,000
Fair Value Option Securities [Abstract]
U.S. Agency Residential Mortgage-backed Securities, Fair Value Option Securities, Fair Value Disclosure	208,900,000		257,040,000		322,180,000
Corporate Debt Securities, Fair Value Option Securities, Fair Value Disclosure			26,486,000		25,772,000
Other Securities, Fair Value Option Securities, Fair Value Disclosure	1,292,000		770,000
Fair Value Option Securities, Fair Value Disclosure	210,192,000		284,296,000		347,952,000
Loans [Abstract]
Mortgage servicing rights, Fair Value Disclosure	0	[4]	0	[4]	0	[4]
Derviative contracts, net of cash margin, assets, Fair Value Disclosure	320,016,000	[5]	326,509,000	[5]	384,996,000	[5]
Other assets - private equity funds, Fair Value Disclosure	0		0		0
Derivative contracts net of cash margin, liabilities, Fair Value DIsclosure	251,836,000	[5]	283,589,000	[5]	305,290,000	[5]
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Trading Securities [Abstract]
U.S. Agency Government Obligations, Trading Securities, Fair Value Disclosure	0		0		0
U.S. Agency Residential Mortgage-backed Securities, Trading Securities, Fair Value Disclosure	0		0		0
Municipal And Other-tax Exempt Securities, Trading Securities, Fair Value Disclosure	0		0		0
Other Trading Securities, Trading Securities, Fair Value Disclosure	0		0		124,000
Trading Securities, Fair Value Disclosure	0		0		124,000
Available for sale securities [Abstract]
U.S. Treasury Securities, Available for Sale Securities, Fair Value DIsclosure	0		0		0
Municipal and Other Tax-exempt Securities, Available for Sale Securities, Fair Value Disclosure	39,007,000		40,702,000		41,977,000
U.S. Agency Residential Mortgage-backed Securities. Available for Sale Securities, Fair Value Disclosure	0		0		0
Privately Issued Residential Mortgage-backed Securities, Available for Sale Securities, Fair Value Disclosure	0		0		0
Commercial Mortgage-backed Securities, Available for Sale Securities, Fair Value Disclosure	0		0
Other Debt Securities, Available for Sale Securities, Fair Value Disclosure	5,193,000		5,399,000		5,900,000
Perpetual Preferred Stock, Available for Sale Securities, Fair Value Disclosure	0		0		0
Equity Securities and Mutual Funds, Available for Sale Securities, Fair Value Disclosure	2,472,000		2,161,000		0
Available for Sale Securities, Fair Value Disclosure	46,672,000		48,262,000		47,877,000
Fair Value Option Securities [Abstract]
U.S. Agency Residential Mortgage-backed Securities, Fair Value Option Securities, Fair Value Disclosure	0		0		0
Corporate Debt Securities, Fair Value Option Securities, Fair Value Disclosure			0		0
Other Securities, Fair Value Option Securities, Fair Value Disclosure	0		0
Fair Value Option Securities, Fair Value Disclosure	0		0		0
Loans [Abstract]
Mortgage servicing rights, Fair Value Disclosure	109,840,000	[4]	100,812,000	[4]	98,138,000	[4]
Derviative contracts, net of cash margin, assets, Fair Value Disclosure	0	[5]	0	[5]	0	[5]
Other assets - private equity funds, Fair Value Disclosure	29,216,000		28,169,000		30,993,000
Derivative contracts net of cash margin, liabilities, Fair Value DIsclosure	$ 0	[5]	$ 0	[5]	$ 0	[5]

[1] Carrying value includes $3.9 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 $9.9 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.

[4] A reconciliation of the beginning and ending fair value of mortgage servicing rights and disclosures of significant assumptions used to determine fair value are presented in Note 6, Mortgage Banking Activities.

[5] See Note 3 for detail of fair value of derivative contracts by contract type.

[6] Represents exchange-traded agricultural derivative contracts.

[7] Represents exchange-traded energy derivative contracts.

[8] Represents exchange-traded energy derivative contracts