Condensed Consolidated Statements of Income - USD ($) shares in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Interest income:
Loans, including fees	$ 308,461,000	$ 315,574,000	$ 319,882,000
Investment securities:
Taxable	18,025,000	16,110,000	15,758,000
Tax-exempt	3,884,000	4,300,000	4,589,000
Federal funds sold and securities purchased under agreements to resell	2,793,000	2,117,000	1,793,000
Total interest income	333,163,000	338,101,000	342,022,000
Interest expense:
Deposits	5,803,000	7,344,000	9,301,000
Federal funds purchased and securities sold under agreements to repurchase	574,000	395,000	357,000
Other borrowings	1,940,000	2,589,000	6,004,000
Total interest expense	8,317,000	10,328,000	15,662,000
Net interest income	324,846,000	327,773,000	326,360,000
Provision for loan losses	6,819,000	5,864,000	6,590,000
Net interest income after provision for loan losses	318,027,000	321,909,000	319,770,000
Noninterest income:
Fees on deposit accounts	82,897,000	74,479,000	69,291,000
Mortgage banking income	20,547,000	21,761,000	16,170,000
Trust and investment services income	19,764,000	20,117,000	18,344,000
Securities gains, net	122,000		(2,000)
Other-than-temporary impairment losses		(489,000)
Recoveries on acquired loans	6,465,000	2,976,000	6,176,000
Amortization of FDIC indemnification asset, net	(5,902,000)	(8,587,000)	(21,895,000)
Other	6,437,000	5,298,000	6,612,000
Total noninterest income	130,330,000	115,555,000	94,696,000
Noninterest expense:
Salaries and employee benefits	164,663,000	161,304,000	158,432,000
Net occupancy expense	21,712,000	21,105,000	22,459,000
Information services expense	20,549,000	17,810,000	15,844,000
Furniture and equipment expense	12,403,000	11,233,000	13,271,000
OREO expense and loan related	6,307,000	9,595,000	11,833,000
Bankcard expense	11,723,000	9,320,000	8,563,000
Amortization of intangibles	7,577,000	8,324,000	8,320,000
Supplies, printing and postage expense	6,279,000	5,919,000	6,937,000
Professional fees	6,702,000	5,533,000	4,960,000
FDIC assessment and other regulatory charges	3,896,000	4,714,000	5,432,000
Advertising and marketing	3,092,000	3,838,000	4,156,000
Merger related expense	5,002,000		23,940,000
Branch consolidation related expenses	3,079,000	6,945,000
Other	21,331,000	21,449,000	18,891,000
Total noninterest expense	294,315,000	287,089,000	303,038,000
Earnings:
Income before provision for income taxes	154,042,000	150,375,000	111,428,000
Provision for income taxes	52,760,000	50,902,000	35,991,000
Net income	101,282,000	99,473,000	75,437,000
Preferred stock dividends			1,073,000
Net income	$ 101,282,000	$ 99,473,000	$ 74,364,000
Earnings per common share:
Basic (in dollars per share)	$ 4.22	$ 4.15	$ 3.11
Diluted (in dollars per share)	4.18	4.11	3.08
Dividends per common share (in dollars per share)	$ 1.21	$ 0.98	$ 0.82
Weighted-average common shares outstanding:
Basic (in shares)	23,998	23,966	23,897
Diluted (in shares)	24,219	24,224	24,154