Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Loans including fees:
Taxable		$ 515,980	$ 569,718	$ 508,293
Nontaxable		13,908	15,919	16,299
Investment securities:
Taxable		98,953	113,832	80,168
Nontaxable		33,899	29,248	26,655
Money market and other interest-earning investments		568	1,670	630
Total interest income		663,308	730,387	632,045
Interest Expense
Deposits		28,169	69,364	41,277
Federal funds purchased and interbank borrowings		1,296	5,656	4,793
Securities sold under agreements to repurchase		854	2,517	1,962
Federal Home Loan Bank advances		27,274	37,452	34,925
Other borrowings		9,621	11,125	11,486
Total interest expense		67,214	126,114	94,443
Net interest income		596,094	604,273	537,602
Provision for loan losses	[1]	38,395	4,747	6,966
Net interest income after provision for loan losses		557,699	599,526	530,636
Noninterest Income
Wealth management fees		36,806	37,072	36,863
Service charges on deposit accounts		35,081	44,915	44,026
Debit card and ATM fees		20,178	21,652	20,216
Mortgage banking revenue		62,775	26,622	17,657
Investment product fees		21,614	21,785	20,539
Capital markets income		22,480	13,270	4,934
Company-owned life insurance		12,031	11,539	10,584
Debt securities gains (losses), net		10,767	1,923	2,060
Net gain on banking center divestitures		0	0	13,989
Other income		17,542	20,539	24,437
Total noninterest income		239,274	199,317	195,305
Noninterest Expense
Salaries and employee benefits		293,590	289,452	281,275
Occupancy		55,316	55,255	51,941
Equipment		16,690	16,903	14,861
Marketing		10,874	15,898	15,847
Data processing		41,086	37,589	36,170
Communication		9,731	10,702	10,846
Professional fees		15,755	22,854	14,503
FDIC assessment		6,722	6,030	10,638
Amortization of intangibles		14,091	16,911	14,442
Amortization of tax credit investments		18,788	2,749	22,949
Other expense		58,774	34,144	43,789
Total noninterest expense		541,417	508,487	517,261
Income before income taxes		255,556	290,356	208,680
Income tax expense		29,147	52,150	17,850
Net income		$ 226,409	$ 238,206	$ 190,830
Net income per common share - basic (in dollars per share)		$ 1.37	$ 1.39	$ 1.23
Net income per common share - diluted (in dollars per share)		$ 1.36	$ 1.38	$ 1.22
Weighted average number of common shares outstanding - basic (in shares)		165,509	171,907	155,675
Weighted average number of common shares outstanding - diluted (in shares)		166,177	172,687	156,539
Dividends per common share (in dollars per share)		$ 0.56	$ 0.52	$ 0.52

[1] Beginning January 1, 2020, calculation is based on current expected loss methodology. Prior to January 1, 2020, calculation was based on incurred loss methodology.