Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Interest income:
Loans, including fees	$ 772,030	$ 625,023	$ 583,751
Loans held for sale	851	1,022	678
Securities-taxable	102,013	91,099	90,522
Securities-tax exempt	22,235	13,222	3,447
Short-term investments	3,452	1,801	1,248
Total interest income	900,581	732,167	679,646
Interest expense:
Deposits	76,546	48,934	33,876
Short-term borrowings	15,735	4,065	1,078
Long-term debt	15,988	20,052	19,518
Total interest expense	108,269	73,051	54,472
Net interest income	792,312	659,116	625,174
Provision for loan losses	58,968	110,659	73,038
Net interest income after provision for loan losses	733,344	548,457	552,136
Noninterest income:
Service charges on deposit accounts	83,166	74,187	72,813
Trust fees	44,538	46,589	45,627
Bank card and ATM fees	53,779	47,427	46,480
Investment and annuity fees	20,529	18,477	20,669
Secondary mortgage market operations	15,209	16,282	12,579
Insurance commissions and fees	3,212	4,501	8,567
Amortization of loss share receivable	(2,427)	(5,918)	(5,747)
Other income	49,775	47,482	35,961
Securities transactions		1,754	335
Total noninterest income	267,781	250,781	237,284
Noninterest expense:
Compensation expense	320,096	287,783	278,661
Employee benefits	56,568	55,884	54,880
Personnel expense	376,664	343,667	333,541
Net occupancy expense	47,869	41,296	44,842
Equipment expense	14,841	13,663	15,494
Data processing expense	66,385	58,619	55,590
Professional services expense	40,235	29,561	40,198
Amortization of intangibles	22,417	19,781	24,184
Telecommunications and postage	14,686	13,146	14,127
Deposit insurance and regulatory fees	29,627	23,499	16,736
Other real estate (income) expense, net	(2,669)	(3,481)	2,740
Other expense	82,636	72,564	72,203
Total noninterest expense	692,691	612,315	619,655
Income before income taxes	308,434	186,923	169,765
Income taxes	92,802	37,627	38,304
Net income	$ 215,632	$ 149,296	$ 131,461
Earnings per common share-basic	$ 2.49	$ 1.87	$ 1.64
Earnings per common share-diluted	2.48	1.87	1.64
Dividends paid per share	$ 0.96	$ 0.96	$ 0.96
Weighted average shares outstanding-basic	84,695	77,850	78,197
Weighted average shares outstanding-diluted	84,963	77,949	78,307