Consolidated Statements of Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Interest income
Loans and leases	$ 1,332,720	$ 1,217,306	$ 1,073,051
Investment securities interest and dividend income	144,459	160,460	150,709
Overnight investments	6,847	26,245	21,997
Total interest income	1,484,026	1,404,011	1,245,757
Interest expense
Deposits	66,635	76,254	22,483
Securities sold under customer repurchase agreements	1,610	1,995	1,594
Federal Home Loan Bank borrowings	9,763	5,472	5,801
Subordinated debt	16,074	7,099	6,277
Other borrowings	1,775	1,822	702
Total interest expense	95,857	92,642	36,857
Net interest income	1,388,169	1,311,369	1,208,900
Provision for credit losses	58,352	31,441	28,468
Net interest income after provision for credit losses	1,329,817	1,279,928	1,180,432
Noninterest income
Merchant services, net	24,122	24,304	24,504
Realized gains on investment securities available for sale, net	60,253	7,115	351
Marketable equity securities gains (losses), net	29,395	20,625	(7,610)
Gain on extinguishment of debt	0	0	26,553
Other	7,446	18,431	19,700
Total noninterest income	476,750	415,861	400,149
Noninterest expense
Salaries and wages	590,020	551,112	527,691
Employee benefits	132,244	120,501	118,203
Occupancy expense	117,169	111,179	109,169
Equipment expense	115,535	112,290	102,909
Processing fees paid to third parties	44,791	29,552	30,017
FDIC insurance expense	12,701	10,664	18,890
Collection and foreclosure-related expenses	13,658	11,994	16,567
Merger-related expenses	17,450	17,166	6,462
Other	145,117	139,283	147,063
Total noninterest expense	1,188,685	1,103,741	1,076,971
Income before income taxes	617,882	592,048	503,610
Income taxes	126,159	134,677	103,297
Net income	491,723	457,371	400,313
Less: Preferred stock dividends	14,062	0	0
Net income available to common shareholders	$ 477,661	$ 457,371	$ 400,313
Average shares outstanding (in shares)	10,056,654	11,141,069	11,938,439
Net income per share	$ 47.50	$ 41.05	$ 33.53
Cash dividends (in dollars per share)	$ 1.67	$ 1.60	$ 1.45
Wealth management services
Noninterest income
Revenue from contracts with customers	$ 102,776	$ 99,241	$ 97,966
Service charges on deposit accounts
Noninterest income
Revenue from contracts with customers	87,662	105,191	105,486
Cardholder services, net
Noninterest income
Revenue from contracts with customers	74,291	69,078	65,478
Mortgage income
Noninterest income
Revenue from contracts with customers	39,592	21,126	16,433
Merchant services, net
Noninterest income
Revenue from contracts with customers	30,911	31,644	30,606
Insurance commissions
Noninterest income
Revenue from contracts with customers	14,544	12,810	12,702
ATM income
Noninterest income
Revenue from contracts with customers	$ 5,758	$ 6,296	$ 7,980