Consolidated Balance Sheets (Unaudited) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012		Sep. 30, 2012
Assets [Abstract]
Cash and due from banks	$ 1,133,771		$ 1,266,834		$ 596,590
Funds sold and resell agreements	27,214		19,405		18,904
Trading securities	150,887		214,102		204,242
Investment securities	644,225	[1]	499,534	[2]	432,114	[3]
Available for sale securities	10,372,903		11,287,221		11,506,434
Fair value option securities	167,860		284,296		331,887
Residential mortgage loans held for sale	230,511		293,762		325,102
Loans	12,350,100		12,311,456		11,832,367
Allowance for loan losses	(194,325)		(215,507)		(233,756)
Loans, net of allowance	12,155,775		12,095,949		11,598,611
Premises and equipment, net	275,347		265,920		259,195
Receivables	108,435		114,185		116,243
Goodwill	359,759		361,979		358,962
Intangible assets, net	25,407		28,192		33,196
Mortgage servicing rights, net	140,863		100,812		89,653
Real estate and other repossessed assets, net of allowance	108,122		103,791		104,128
Bankers' acceptances	748		605		1,605
Derivative contracts	377,325		338,106		435,653
Cash surrender value of bank-owned life insurance	282,490		274,531		271,830
Receivable on unsettled securities sales	93,020		211,052		32,480
Other assets	511,705		388,355		400,812
Total assets	27,166,367		28,148,631		27,117,641
Deposits [Abstract]
Noninterest-bearing demand deposits	7,331,976		8,038,286		6,848,401
Interest-bearing deposits: [Abstract]
Transaction	9,119,810		9,888,038		9,002,567
Savings	319,849		284,744		269,573
Time	2,720,020		2,967,992		3,022,326
Total deposits	19,491,655		21,179,060		19,142,867
Funds purchased	992,345		1,167,416		1,680,626
Repurchase agreements	782,418		887,030		1,109,696
Other borrowings	1,837,181		651,775		639,254
Subordinated debentures	347,758		347,633		347,592
Accrued interest, taxes and expense	182,076		176,678		182,410
Bankers' acceptances	748		605		1,605
Derivative contracts	232,544		283,589		254,422
Due on unsettled securities purchases	114,259		297,453		556,998
Other liabilities	158,409		163,711		189,696
Total liabilities	24,139,393		25,154,950		24,105,166
Shareholders' equity: [Abstract]
Common stock	4		4		4
Capital surplus	890,433		859,278		849,390
Retained earnings	2,303,688		2,137,541		2,148,292
Treasury stock	(200,255)		(188,883)		(184,422)
Accumulated other comprehensive income (loss)	(2,626)		149,920		162,393
Total shareholders' equity	2,991,244		2,957,860		2,975,657
Non-controlling interest	35,730		35,821		36,818
Total equity	3,026,974		2,993,681		3,012,475
Total liabilities and equity	$ 27,166,367		$ 28,148,631		$ 27,117,641

[1] Carrying value includes $2.3 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.

[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 $6.2 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.