Consolidated Balance Sheets (Unaudited) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013		Mar. 31, 2013
Assets [Abstract]
Cash and due from banks	$ 645,435		$ 512,931		$ 458,471
Interest-bearing cash and cash equivalents	708,571		574,282		487,146
Trading securities	86,571		91,616		206,598
Investment securities	668,976	[1]	677,878	[2]	589,271	[3]
Available for sale securities	9,933,723		10,147,162		11,059,145
Fair value option securities	160,884		167,125		210,192
Restricted equity securities	85,643		85,240		119,988
Residential mortgage loans held for sale	226,512		200,546		286,211
Loans	13,077,854		12,792,264		12,093,564
Allowance for loan losses	(188,318)		(185,396)		(205,965)
Loans, net of allowance	12,889,536		12,606,868		11,887,599
Premises and equipment, net	279,257		277,849		270,130
Receivables	114,437		117,126		116,028
Goodwill	364,570		359,759		359,759
Intangible assets, net	31,561		24,564		27,117
Mortgage servicing rights, net	153,774		153,333		109,840
Real estate and other repossessed assets, net of allowance	95,515		92,272		102,701
Derivative contracts	218,507		265,012		320,473
Cash surrender value of bank-owned life insurance	286,932		284,801		277,776
Receivable on unsettled securities sales	18,199		17,174		190,688
Other assets	396,111		359,894		368,025
Total assets	27,364,714		27,015,432		27,447,158
Deposits [Abstract]
Noninterest-bearing demand deposits	7,472,287		7,316,277		6,900,860
Interest-bearing deposits: [Abstract]
Transaction	9,899,656		9,934,051		9,742,302
Savings	355,596		323,006		317,075
Time	2,662,174		2,695,993		2,900,054
Total deposits	20,389,713		20,269,327		19,860,291
Funds purchased	1,166,178		868,081		853,843
Repurchase agreements	777,108		813,454		806,526
Other borrowings	1,031,693		1,040,353		1,733,047
Subordinated debentures	347,846		347,802		347,674
Accrued interest, taxes and expense	160,351		194,870		192,358
Derivative contracts	185,499		247,185		251,836
Due on unsettled securities purchases	39,641		45,740		158,984
Other liabilities	122,086		133,647		194,707
Total liabilities	24,220,115		23,960,459		24,399,266
Shareholders' equity: [Abstract]
Common stock	4		4		4
Capital surplus	913,642		898,586		876,368
Retained earnings	2,398,636		2,349,428		2,199,722
Treasury stock	(209,152)		(202,346)		(197,519)
Accumulated other comprehensive income (loss)	6,795		(25,623)		133,383
Total shareholders' equity	3,109,925		3,020,049		3,011,958
Non-controlling interests	34,674		34,924		35,934
Total equity	3,144,599		3,054,973		3,047,892
Total liabilities and equity	$ 27,364,714		$ 27,015,432		$ 27,447,158

[1] Carrying value includes $1.4 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 $3.9 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.