Consolidated Statements of Income (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Interest income:
Loans, including fees	$ 440,958	$ 415,230	$ 401,364
Securities:
Taxable	93,087	97,873	132,432
Tax-exempt	156,618	122,031	93,412
Interest-bearing deposits	10,725	7,284	4,300
Federal funds sold and resell agreements	83	82	104
Total interest income	701,471	642,500	631,612
Interest expense:
Deposits	11,022	14,459	18,099
Federal funds purchased and repurchase agreements	134	121	140
Junior subordinated deferrable interest debentures	2,488	6,426	6,806
Other long-term borrowings	893	939	1,706
Total interest expense	14,537	21,945	26,751
Net interest income	686,934	620,555	604,861
Provision for loan losses	16,314	20,582	10,080
Net interest income after provision for loan losses	670,620	599,973	594,781
Non-interest income:
Trust and investment management fees	106,237	91,375	83,317
Service charges on deposit accounts	81,946	81,432	83,392
Insurance commissions and fees	45,115	43,140	39,948
Interchange and debit card transaction fees	18,372	16,979	16,933
Other charges, commissions and fees	36,180	34,185	30,180
Net gain (loss) on securities transactions	38	1,176	4,314
Other	32,256	34,531	30,703
Total non-interest income	320,144	302,818	288,787
Non-interest expense:
Salaries and wages	292,349	273,692	258,752
Employee benefits	60,151	62,407	57,635
Net occupancy	55,745	50,468	48,975
Furniture and equipment	62,087	58,443	55,279
Deposit insurance	13,232	11,682	11,087
Intangible amortization	3,520	3,141	3,896
Other	167,656	152,077	139,469
Total non-interest expense	654,740	611,910	575,093
Income before income taxes	336,024	290,881	308,475
Income taxes	58,047	53,015	70,523
Net income	277,977	237,866	237,952
Preferred stock dividends	8,063	6,719	0
Net income available to common shareholders	$ 269,914	$ 231,147	$ 237,952
Earnings per common share:
Basic (in dollars per share)	$ 4.32	$ 3.82	$ 3.87
Diluted (in dollars per share)	$ 4.29	$ 3.80	$ 3.86