Consolidated Balance Sheets (Unaudited) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013		Dec. 31, 2012		Jun. 30, 2012
Assets [Abstract]
Cash and due from banks	$ 1,026,497		$ 1,266,834		$ 628,092
Funds sold and resell agreements	51,888		19,405		11,171
Trading securities	190,591		214,102		149,317
Investment securities	615,790	[1]	499,534	[2]	412,479	[3]
Available for sale securities	10,698,074		11,287,221		10,395,415
Fair value option securities	205,756		284,296		325,177
Residential mortgage loans held for sale	301,057		293,762		259,174
Loans	12,440,782		12,311,456		11,576,431
Allowance for loan losses	(203,124)		(215,507)		(231,669)
Loans, net of allowance	12,237,658		12,095,949		11,344,762
Premises and equipment, net	271,191		265,920		261,508
Receivables	136,605		114,185		121,944
Goodwill	359,759		361,979		335,601
Intangible assets, net	26,242		28,192		9,098
Mortgage servicing rights, net	132,889		100,812		91,783
Real estate and other repossessed assets, net of allowance	110,112		103,791		105,708
Bankers' acceptances	198		605		2,873
Derivative contracts	546,206		338,106		366,204
Cash surrender value of bank-owned life insurance	280,047		274,531		269,093
Receivable on unsettled securities trades	182,147		211,052		32,876
Other assets	435,493		388,355		453,771
Total assets	27,808,200		28,148,631		25,576,046
Liabilities [Abstract]
Noninterest-bearing demand deposits	7,145,323		8,038,286		6,440,375
Interest-bearing deposits: [Abstract]
Transaction	9,266,560		9,888,038		8,551,874
Savings	316,375		284,744		261,998
Time	2,767,972		2,967,992		3,107,950
Total deposits	19,496,230		21,179,060		18,362,197
Funds purchased	747,165		1,167,416		1,453,750
Repurchase agreements	845,106		887,030		1,136,948
Other borrowings	2,481,644		651,775		58,056
Subordinated debentures	347,716		347,633		353,378
Accrued interest, taxes and expense	175,677		176,678		140,434
Bankers' acceptances	198		605		2,873
Derivative contracts	521,991		283,589		370,053
Due on unsettled securities trades	49,369		297,453		603,800
Other liabilities	150,222		163,711		171,836
Total liabilities	24,815,318		25,154,950		22,653,325
Shareholders' equity: [Abstract]
Common stock	4		4		4
Capital surplus	884,238		859,278		836,065
Retained earnings	2,253,810		2,137,541		2,086,565
Treasury stock	(199,429)		(188,883)		(175,890)
Accumulated other comprehensive income	19,014		149,920		139,190
Total shareholders' equity	2,957,637		2,957,860		2,885,934
Non-controlling interest	35,245		35,821		36,787
Total equity	2,992,882		2,993,681		2,922,721
Total liabilities and equity	$ 27,808,200		$ 28,148,631		$ 25,576,046

[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.