Consolidated Statements of Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Interest income:
Loans, including fees	$ 458,094	$ 433,872	$ 440,958
Securities:
Taxable	103,025	112,601	93,087
Tax-exempt	210,918	194,793	156,618
Interest-bearing deposits	16,103	8,123	10,725
Federal funds sold and resell agreements	272	107	83
Total interest income	788,412	749,496	701,471
Interest expense:
Deposits	7,248	9,024	11,022
Federal funds purchased and repurchase agreements	204	167	134
Junior subordinated deferrable interest debentures	3,281	2,725	2,488
Other long-term borrowings	1,343	948	893
Total interest expense	12,076	12,864	14,537
Net interest income	776,336	736,632	686,934
Provision for loan losses	51,673	51,845	16,314
Net interest income after provision for loan losses	724,663	684,787	670,620
Non-interest income:
Trust and investment management fees	104,240	105,512	106,237
Service charges on deposit accounts	81,203	81,350	81,946
Insurance commissions and fees	47,154	48,926	45,115
Interchange and debit card transaction fees	21,369	19,666	18,372
Other charges, commissions and fees	39,623	37,551	36,180
Net gain on securities transactions	14,975	69	38
Other	41,144	35,656	32,256
Total non-interest income	349,708	328,730	320,144
Non-interest expense:
Salaries and wages	318,665	310,504	292,349
Employee benefits	72,615	69,746	60,151
Net occupancy	71,627	65,690	55,745
Furniture and equipment	71,208	64,373	62,087
Deposit insurance	17,428	14,519	13,232
Intangible amortization	2,429	3,325	3,520
Other	178,988	165,561	167,656
Total non-interest expense	732,960	693,718	654,740
Income before income taxes	341,411	319,799	336,024
Income taxes	37,150	40,471	58,047
Net income	304,261	279,328	277,977
Preferred stock dividends	8,063	8,063	8,063
Net income available to common shareholders	$ 296,198	$ 271,265	$ 269,914
Earnings per common share:
Basic (in dollars per share)	$ 4.73	$ 4.31	$ 4.32
Diluted (in dollars per share)	$ 4.70	$ 4.28	$ 4.29