Consolidated Statements of Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Interest income:
Loans, including fees	$ 433,872	$ 440,958	$ 415,230
Securities:
Taxable	112,601	93,087	97,873
Tax-exempt	194,793	156,618	122,031
Interest-bearing deposits	8,123	10,725	7,284
Federal funds sold and resell agreements	107	83	82
Total interest income	749,496	701,471	642,500
Interest expense:
Deposits	9,024	11,022	14,459
Federal funds purchased and repurchase agreements	167	134	121
Junior subordinated deferrable interest debentures	2,725	2,488	6,426
Other long-term borrowings	948	893	939
Total interest expense	12,864	14,537	21,945
Net interest income	736,632	686,934	620,555
Provision for loan losses	51,845	16,314	20,582
Net interest income after provision for loan losses	684,787	670,620	599,973
Non-interest income:
Trust and investment management fees	105,512	106,237	91,375
Service charges on deposit accounts	81,350	81,946	81,432
Insurance commissions and fees	48,926	45,115	43,140
Interchange and debit card transaction fees	19,666	18,372	16,979
Other charges, commissions and fees	37,551	36,180	34,185
Net gain (loss) on securities transactions	69	38	1,176
Other	35,656	32,256	34,531
Total non-interest income	328,730	320,144	302,818
Non-interest expense:
Salaries and wages	310,504	292,349	273,692
Employee benefits	69,746	60,151	62,407
Net occupancy	65,690	55,745	50,468
Furniture and equipment	64,373	62,087	58,443
Deposit insurance	14,519	13,232	11,682
Intangible amortization	3,325	3,520	3,141
Other	165,561	167,656	152,077
Total non-interest expense	693,718	654,740	611,910
Income before income taxes	319,799	336,024	290,881
Income taxes	40,471	58,047	53,015
Net income	279,328	277,977	237,866
Preferred stock dividends	8,063	8,063	6,719
Net income available to common shareholders	$ 271,265	$ 269,914	$ 231,147
Earnings per common share:
Basic (in dollars per share)	$ 4.31	$ 4.32	$ 3.82
Diluted (in dollars per share)	$ 4.28	$ 4.29	$ 3.80