CONSOLIDATED STATEMENTS OF INCOME - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Interest income:
Loans, including fees	$ 919,744,000	$ 955,388,000	$ 850,472,000
Securities:
Taxable	35,663,000	46,649,000	48,192,000
Tax-exempt	58,867,000	51,138,000	35,995,000
Federal funds sold and other	6,768,000	14,761,000	12,058,000
Total interest income	1,021,042,000	1,067,936,000	946,717,000
Interest expense:
Deposits	135,547,000	231,641,000	151,043,000
Securities sold under agreements to repurchase	350,000	570,000	588,000
Federal Home Loan Bank advances and other borrowings	63,357,000	69,583,000	58,744,000
Total interest expense	199,254,000	301,794,000	210,375,000
Net interest income	821,788,000	766,142,000	736,342,000
Provision for credit losses	191,734,000	27,283,000	34,377,000
Net interest income after provision for credit losses	630,054,000	738,859,000	701,965,000
Noninterest income:
Total noninterest income	317,840,000	263,826,000	200,850,000
Noninterest expense:
Salaries and employee benefits	334,483,000	313,359,000	271,673,000
Equipment and occupancy	88,475,000	84,582,000	74,276,000
Other real estate expense, net	8,555,000	4,228,000	723,000
Marketing and other business development	10,693,000	13,251,000	11,712,000
Postage and supplies	7,819,000	8,144,000	7,815,000
Amortization of intangibles	9,793,000	9,908,000	10,549,000
Merger related expenses	0	0	8,259,000
Total other noninterest expense	116,718,000	71,676,000	67,860,000
Total noninterest expense	576,536,000	505,148,000	452,867,000
Income before income taxes	371,358,000	497,537,000	449,948,000
Income tax expense	59,037,000	96,656,000	90,508,000
Net income	312,321,000	400,881,000	359,440,000
Preferred stock dividends	7,596,000	0	0
Net income available to common shareholders	$ 304,725,000	$ 400,881,000	$ 359,440,000
Per share information:
Basic net income per common share	$ 4.04	$ 5.25	$ 4.66
Diluted net income per common share	$ 4.03	$ 5.22	$ 4.64
Weighted average common shares outstanding:
Basic	75,376,489	76,364,303	77,111,372
Diluted	75,654,385	76,763,903	77,449,917
Service charges on deposit accounts
Noninterest income:
Total noninterest income	$ 34,282,000	$ 36,769,000	$ 36,088,000
Investment services
Noninterest income:
Total noninterest income	29,537,000	24,187,000	21,985,000
Insurance sales commissions
Noninterest income:
Total noninterest income	10,055,000	9,344,000	9,331,000
Gain on mortgage loans sold, net
Noninterest income:
Total noninterest income	60,042,000	24,335,000	14,564,000
Investment gains (losses) on sales, net
Noninterest income:
Total noninterest income	986,000	(5,941,000)	(2,254,000)
Trust fees
Noninterest income:
Total noninterest income	16,496,000	14,184,000	13,143,000
Income from equity method investment
Noninterest income:
Total noninterest income	83,539,000	90,111,000	51,222,000
Other noninterest income
Noninterest income:
Total noninterest income	$ 82,903,000	$ 70,837,000	$ 56,771,000