Consolidated Statements of Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Interest income:
Loans, including fees	$ 680,064	$ 741,747	$ 669,002
Securities:
Taxable	93,569	117,082	86,370
Tax-exempt	233,614	233,842	233,358
Interest-bearing deposits	12,893	35,590	56,968
Federal funds sold and resell agreements	895	5,524	5,500
Total interest income	1,021,035	1,133,785	1,051,198
Interest expense:
Deposits	32,018	99,742	75,337
Federal funds purchased and repurchase agreements	4,482	19,675	8,021
Junior subordinated deferrable interest debentures	3,560	5,706	5,291
Subordinated notes	4,656	4,657	4,657
Federal Home Loan Bank advances	318	0	0
Total interest expense	45,034	129,780	93,306
Net interest income	976,001	1,004,005	957,892
Credit loss expense	241,230	33,759	21,685
Net interest income after credit loss expense	734,771	970,246	936,207
Non-interest income:
Trust and investment management fees	129,272	126,722	119,391
Service charges on deposit accounts	80,873	88,983	85,186
Insurance commissions and fees	50,313	52,345	48,967
Interchange and debit card transaction fees	13,470	14,873	13,877
Other charges, commissions and fees	34,825	37,123	37,231
Net gain (loss) on securities transactions	108,989	293	(156)
Other	47,712	43,563	46,790
Total non-interest income	465,454	363,902	351,286
Non-interest expense:
Salaries and wages	387,328	375,029	350,312
Employee benefits	75,676	86,230	77,323
Net occupancy	102,938	89,466	76,788
Technology, furniture and equipment	105,232	91,995	83,102
Deposit insurance	10,502	10,126	16,397
Intangible amortization	918	1,168	1,424
Other	166,310	180,665	173,466
Total non-interest expense	848,904	834,679	778,812
Income before income taxes	351,321	499,469	508,681
Income taxes	20,170	55,870	53,763
Net income	331,151	443,599	454,918
Preferred stock dividends	2,016	8,063	8,063
Redemption of preferred stock	5,514	0	0
Net income available to common shareholders	$ 323,621	$ 435,536	$ 446,855
Earnings per common share:
Basic (in dollars per share)	$ 5.11	$ 6.89	$ 6.97
Diluted (in dollars per share)	$ 5.10	$ 6.84	$ 6.90