Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Assets [Abstract]
Cash and due from banks	$ 550,576		$ 512,931
Interest-bearing cash and cash equivalents	1,925,266		574,282
Trading securities	188,700		91,616
Investment securities	652,360	[1]	677,878	[2]
Available for sale securities	8,978,945		10,147,162
Fair value option securities	311,597		167,125
Restricted equity securities	141,494		85,240
Residential mortgage loans held for sale	304,182		200,546
Loans	14,208,037		12,792,264
Allowance for loan losses	(189,056)		(185,396)
Loans, net of allowance	14,018,981		12,606,868
Premises and Equipment, net	273,833		277,849
Receivables	132,408		117,126
Goodwill	377,780		359,759
Intangible assets, net	34,376		24,564
Mortgage servicing rights	171,976		153,333
Real estate and other repossessed assets, net of allowance	101,861		92,272
Derivative contracts	361,874		265,012
Cash surrender value of bank-owned life insurance	293,978		284,801
Receivable on unsettled securities sales	74,259		17,174
Other assets	195,252		359,894
Total assets	29,089,698		27,015,432
Liabilities [Abstract]
Noninterest-bearing demand deposits	8,066,357		7,316,277
Interest-bearing deposits: [Abstract]
Transaction	10,114,355		9,934,051
Savings	351,431		323,006
Time	2,608,716		2,695,993
Total deposits	21,140,859		20,269,327
Funds purchased	57,031		868,081
Repurchase agreements	1,187,489		813,454
Other borrowings	2,133,774		1,040,353
Subordinated debentures	347,983		347,802
Accrued interest, taxes and expense	120,211		194,870
Derivative contracts	354,554		247,185
Due on unsettled securities purchases	290,540		45,740
Other liabilities	121,051		133,647
Total liabilities	25,753,492		23,960,459
Shareholders' equity: [Abstract]
Common stock	4		4
Capital surplus	954,644		898,586
Retained earnings	2,530,837		2,349,428
Treasury stock	(239,979)		(202,346)
Accumulated other comprehensive income (loss)	56,673		(25,623)
Total shareholders' equity	3,302,179		3,020,049
Non-controlling interests	34,027		34,924
Total equity	3,336,206		3,054,973
Total liabilities and equity	$ 29,089,698		$ 27,015,432

[1] Carrying value includes $615 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 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.