Consolidated Balance Sheets (Unaudited) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014		Dec. 31, 2013		Sep. 30, 2013
Assets [Abstract]
Cash and due from banks	$ 557,658		$ 512,931		$ 625,671
Interest-bearing cash and cash equivalents	2,007,901		574,282		535,313
Trading securities	169,712		91,616		150,887
Investment securities	655,091	[1]	677,878	[2]	644,225	[3]
Available for sale securities	9,306,886		10,147,162		10,372,903
Fair value option securities	175,761		167,125		167,860
Restricted equity securities	189,587		85,240		125,540
Residential mortgage loans held for sale	373,253		200,546		230,511
Loans	13,683,739		12,792,264		12,350,100
Allowance for loan losses	(191,244)		(185,396)		(194,325)
Loans, net of allowance	13,492,495		12,606,868		12,155,775
Premises and equipment, net	275,718		277,849		275,347
Receivables	114,374		117,126		108,435
Goodwill	377,780		359,759		359,759
Intangible assets, net	35,476		24,564		25,407
Mortgage servicing rights	173,286		153,333		140,863
Real estate and other repossessed assets, net of allowance	97,871		92,272		108,122
Derivative contracts	360,809		265,012		377,325
Cash surrender value of bank-owned life insurance	291,583		284,801		282,490
Receivable on unsettled securities sales	94,881		17,174		93,020
Other assets	354,898		359,894		386,914
Total assets	29,105,020		27,015,432		27,166,367
Deposits [Abstract]
Noninterest-bearing demand deposits	8,038,129		7,316,277		7,331,976
Interest-bearing deposits: [Abstract]
Transaction	9,244,709		9,934,051		9,119,810
Savings	341,638		323,006		319,849
Time	2,664,580		2,695,993		2,720,020
Total deposits	20,289,056		20,269,327		19,491,655
Funds purchased	85,135		868,081		992,345
Repurchase agreements	1,026,009		813,454		782,418
Other borrowings	3,484,487		1,040,353		1,837,181
Subordinated debentures	347,936		347,802		347,758
Accrued interest, taxes and expense	100,664		194,870		182,076
Derivative contracts	348,687		247,185		232,544
Due on unsettled securities purchases	8,126		45,740		114,259
Other liabilities	137,608		133,647		159,157
Total liabilities	25,827,708		23,960,459		24,139,393
Shareholders' equity: [Abstract]
Common stock	4		4		4
Capital surplus	948,305		898,586		890,433
Retained earnings	2,495,338		2,349,428		2,303,688
Treasury stock	(223,849)		(202,346)		(200,255)
Accumulated other comprehensive income (loss)	23,295		(25,623)		(2,626)
Total shareholders' equity	3,243,093		3,020,049		2,991,244
Non-controlling interests	34,219		34,924		35,730
Total equity	3,277,312		3,054,973		3,026,974
Total liabilities and equity	$ 29,105,020		$ 27,015,432		$ 27,166,367

[1] Carrying value includes $822 thousand 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 $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.