Consolidated Balance Sheets (Unaudited) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014		Dec. 31, 2013		Jun. 30, 2013
Assets [Abstract]
Cash and due from banks	$ 615,479		$ 512,931		$ 507,551
Interest-bearing cash and cash equivalents	732,395		574,282		570,836
Trading securities	101,097		91,616		190,591
Investment securities	649,937	[1]	677,878	[2]	615,790	[3]
Available for sale securities	9,699,146		10,147,162		10,698,074
Fair value option securities	185,674		167,125		205,756
Restricted equity securities	91,213		85,240		157,847
Residential mortgage loans held for sale	325,875		200,546		301,057
Loans	13,426,858		12,792,264		12,440,782
Allowance for loan losses	(190,690)		(185,396)		(203,124)
Loans, net of allowance	13,236,168		12,606,868		12,237,658
Premises and equipment, net	280,286		277,849		271,191
Receivables	115,991		117,126		136,605
Goodwill	377,780		359,759		359,759
Intangible assets, net	36,576		24,564		26,242
Mortgage servicing rights	155,740		153,333		132,889
Real estate and other repossessed assets, net of allowance	100,111		92,272		110,112
Derivative contracts	357,680		265,012		546,206
Cash surrender value of bank-owned life insurance	289,231		284,801		280,047
Receivable on unsettled securities sales	14,025		17,174		182,147
Other assets	479,366		359,894		277,842
Total assets	27,843,770		27,015,432		27,808,200
Deposits [Abstract]
Noninterest-bearing demand deposits	7,908,005		7,316,277		7,145,323
Interest-bearing deposits: [Abstract]
Transaction	9,698,404		9,934,051		9,266,560
Savings	349,629		323,006		316,375
Time	2,615,826		2,695,993		2,767,972
Total deposits	20,571,864		20,269,327		19,496,230
Funds purchased	705,573		868,081		747,165
Repurchase agreements	1,072,375		813,454		845,106
Other borrowings	1,231,662		1,040,353		2,481,644
Subordinated debentures	347,890		347,802		347,716
Accrued interest, taxes and expense	100,227		194,870		175,677
Derivative contracts	297,851		247,185		521,991
Due on unsettled securities purchases	124,537		45,740		49,369
Other liabilities	144,145		133,647		150,420
Total liabilities	24,596,124		23,960,459		24,815,318
Shareholders' equity: [Abstract]
Common stock	4		4		4
Capital surplus	938,665		898,586		884,238
Retained earnings	2,447,118		2,349,428		2,253,810
Treasury stock	(222,686)		(202,346)		(199,429)
Accumulated other comprehensive income (loss)	49,416		(25,623)		19,014
Total shareholders' equity	3,212,517		3,020,049		2,957,637
Non-controlling interests	35,129		34,924		35,245
Total equity	3,247,646		3,054,973		2,992,882
Total liabilities and equity	$ 27,843,770		$ 27,015,432		$ 27,808,200

[1] Carrying value includes $1.1 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 $1.8 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 $3.0 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.