Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Interest income:
Loans, including fees	$ 971,735	$ 877,875	$ 772,030
Loans held for sale	1,876	946	851
Securities-taxable	127,459	124,720	102,013
Securities-tax exempt	20,757	21,951	22,235
Short-term investments	3,955	2,776	3,452
Total interest income	1,125,782	1,028,268	900,581
Interest expense:
Deposits	187,988	130,715	76,546
Short-term borrowings	30,766	36,096	15,735
Long-term debt	11,811	12,619	15,988
Total interest expense	230,565	179,430	108,269
Net interest income	895,217	848,838	792,312
Provision for credit losses	47,708	36,116	58,968
Net interest income after provision for credit losses	847,509	812,722	733,344
Noninterest income:
Net gain on sales of assets	593	24,654	7,478
Securities transactions		(25,480)
Other income	53,938	43,786	39,870
Total noninterest income	315,907	285,140	267,781
Noninterest expense:
Compensation expense	362,083	330,968	320,096
Employee benefits	77,796	73,727	71,817
Personnel expense	439,879	404,695	391,913
Net occupancy expense	50,936	47,795	47,869
Equipment expense	18,393	16,367	14,841
Data processing expense	82,981	74,129	66,385
Professional services expense	45,007	41,579	40,235
Amortization of intangibles	20,844	22,050	22,417
Deposit insurance and regulatory fees	19,512	31,423	29,627
Other real estate (income) expense	671	(2,985)	(2,669)
Other expense	92,454	80,693	82,073
Total noninterest expense	770,677	715,746	692,691
Income before income taxes	392,739	382,116	308,434
Income taxes	65,359	58,346	92,802
Net income	$ 327,380	$ 323,770	$ 215,632
Earnings per common share - basic	$ 3.72	$ 3.72	$ 2.49
Earnings per common share - diluted	3.72	3.72	2.48
Dividends paid per share	$ 1.08	$ 1.02	$ 0.96
Weighted average shares outstanding-basic	86,488	85,355	84,695
Weighted average shares outstanding-diluted	86,599	85,521	84,963
Service charges on deposit accounts
Noninterest income:
Service charges on deposit accounts	$ 86,364	$ 85,272	$ 83,166
Trust fees
Noninterest income:
Service charges on deposit accounts	61,609	55,488	44,538
Bank card and ATM fees
Noninterest income:
Service charges on deposit accounts	66,976	60,440	53,779
Investment and annuity fees and insurance commissions
Noninterest income:
Service charges on deposit accounts	26,574	25,348	23,741
Secondary mortgage market operations
Noninterest income:
Service charges on deposit accounts	$ 19,853	$ 15,632	$ 15,209