Consolidated Balance Sheets (Unaudited) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012		Mar. 31, 2012
Assets [Abstract]
Cash and due from banks	$ 928,035		$ 1,266,834		$ 691,697
Funds sold and resell agreements	17,582		19,405		14,609
Trading securities	206,598		214,102		128,376
Investment securities	589,271	[1]	499,534	[2]	427,259	[3]
Available for sale securities	11,059,145		11,287,221		10,186,597
Fair value option securities	210,192		284,296		347,952
Residential mortgage loans held for sale	286,211		293,762		247,039
Loans	12,093,564		12,311,456		11,577,444
Allowance for loan losses	(205,965)		(215,507)		(244,209)
Loans, net of allowance	11,887,599		12,095,949		11,333,235
Premises and equipment, net	270,130		265,920		263,579
Receivables	116,028		114,185		138,325
Goodwill	359,759		361,979		335,601
Intangible assets, net	27,117		28,192		9,645
Mortgage servicing rights, net	109,840		100,812		98,138
Real estate and other repossessed assets, net of allowance	102,701		103,791		115,790
Bankers' acceptances	1,762		605		3,493
Derivative contracts	320,473		338,106		384,996
Cash surrender value of bank-owned life insurance	277,776		274,531		266,227
Receivable on unsettled securities trades	190,688		211,052		511,288
Other assets	486,251		388,355		380,327
Total assets	27,447,158		28,148,631		25,884,173
Liabilities [Abstract]
Noninterest-bearing demand deposits	6,900,860		8,038,286		6,189,172
Interest-bearing deposits: [Abstract]
Transaction	9,742,302		9,888,038		8,908,397
Savings	317,075		284,744		259,619
Time	2,900,054		2,967,992		3,166,099
Total deposits	19,860,291		21,179,060		18,523,287
Funds purchased	853,843		1,167,416		1,784,940
Repurchase agreements	806,526		887,030		1,162,546
Other borrowings	1,733,047		651,775		209,230
Subordinated debentures	347,674		347,633		394,760
Accrued interest, taxes and expense	192,358		176,678		180,840
Bankers' acceptances	1,762		605		3,493
Derivative contracts	251,836		283,589		305,290
Due on unsettled securities trades	158,984		297,453		305,166
Other liabilities	192,945		163,711		144,220
Total liabilities	24,399,266		25,154,950		23,013,772
Shareholders' equity: [Abstract]
Common stock	4		4		4
Capital surplus	876,368		859,278		829,991
Retained earnings	2,199,722		2,137,541		2,014,599
Treasury stock	(197,519)		(188,883)		(171,593)
Accumulated other comprehensive income	133,383		149,920		161,418
Total shareholders' equity	3,011,958		2,957,860		2,834,419
Non-controlling interest	35,934		35,821		35,982
Total equity	3,047,892		2,993,681		2,870,401
Total liabilities and equity	$ 27,447,158		$ 28,148,631		$ 25,884,173

[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.