Condensed Consolidated Statements of Income - USD ($) shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Interest income:
Loans, including fees	$ 389,535,000	$ 308,461,000	$ 315,574,000
Investment securities:
Taxable	28,165,000	18,025,000	16,110,000
Tax-exempt	5,591,000	3,884,000	4,300,000
Federal funds sold and securities purchased under agreements to resell	2,709,000	2,793,000	2,117,000
Total interest income	426,000,000	333,163,000	338,101,000
Interest expense:
Deposits	12,353,000	5,803,000	7,344,000
Federal funds purchased and securities sold under agreements to repurchase	1,080,000	574,000	395,000
Other borrowings	3,581,000	1,940,000	2,589,000
Total interest expense	17,014,000	8,317,000	10,328,000
Net interest income	408,986,000	324,846,000	327,773,000
Provision for loan losses	11,890,000	6,819,000	5,864,000
Net interest income after provision for loan losses	397,096,000	318,027,000	321,909,000
Noninterest income:
Fees on deposit accounts	89,882,000	82,897,000	74,479,000
Mortgage banking income	17,954,000	20,547,000	21,761,000
Trust and investment services income	25,401,000	19,764,000	20,117,000
Securities gains, net	1,421,000	122,000
Other-than-temporary impairment on securities	(753,000)		(489,000)
Recoveries on acquired loans	8,572,000	6,465,000	2,976,000
Amortization of FDIC indemnification asset, net		(5,902,000)	(8,587,000)
Other	6,670,000	6,437,000	5,298,000
Total noninterest income	149,147,000	130,330,000	115,555,000
Noninterest expense:
Salaries and employee benefits	194,446,000	164,663,000	161,304,000
Net occupancy expense	25,357,000	21,712,000	21,105,000
Information services expense	25,462,000	20,549,000	17,810,000
Furniture and equipment expense	15,568,000	12,403,000	11,233,000
OREO expense and loan related	6,721,000	6,307,000	9,595,000
Bankcard expense	11,298,000	11,723,000	9,320,000
Amortization of intangibles	10,353,000	7,577,000	8,324,000
Supplies, printing and postage expense	6,148,000	6,279,000	5,919,000
Professional fees	5,975,000	6,702,000	5,533,000
FDIC assessment and other regulatory charges	3,924,000	3,896,000	4,714,000
Advertising and marketing	3,963,000	3,092,000	3,838,000
Merger related expense	44,503,000	8,081,000	6,945,000
Other	23,720,000	21,331,000	21,449,000
Total noninterest expense	377,438,000	294,315,000	287,089,000
Earnings:
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest, Total	168,805,000	154,042,000	150,375,000
Provision for income taxes	81,251,000	52,760,000	50,902,000
Net income	87,554,000	101,282,000	99,473,000
Net income	$ 87,554,000	$ 101,282,000	$ 99,473,000
Earnings per common share:
Basic (in dollars per share)	$ 2.95	$ 4.22	$ 4.15
Diluted (in dollars per share)	2.93	4.18	4.11
Dividends per common share (in dollars per share)	$ 1.32	$ 1.21	$ 0.98
Weighted-average common shares outstanding:
Basic (in shares)	29,686	23,998	23,966
Diluted (in shares)	29,922	24,219	24,224