Consolidated Statements of Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Interest income
Loans and leases	$ 1,217,306	$ 1,073,051	$ 955,637
Investment securities interest and dividend income	160,460	150,709	121,207
Overnight investments	26,245	21,997	26,846
Total interest income	1,404,011	1,245,757	1,103,690
Interest expense
Deposits	76,254	22,483	16,196
Securities sold under customer repurchase agreements	1,995	1,594	1,767
Federal Home Loan Bank borrowings	5,472	5,801	19,915
Subordinated debentures	7,099	6,277	5,213
Other borrowings	1,822	702	703
Total interest expense	92,642	36,857	43,794
Net interest income	1,311,369	1,208,900	1,059,896
Provision for loan and lease losses	31,441	28,468	25,692
Net interest income after provision for loan and lease losses	1,279,928	1,180,432	1,034,204
Noninterest income
Realized gains on investment securities available for sale, net	21,126	16,433	23,251
Gain on acquisitions	20,625	(7,610)	0
Realized gains on investment securities available for sale, net	7,115	351	4,293
Gain on extinguishment of debt	0	26,553	12,483
Gain on acquisitions	0	0	134,745
Other	18,431	19,700	29,081
Total noninterest income	415,861	400,149	521,963
Noninterest expense
Salaries and wages	551,112	527,691	490,610
Employee benefits	120,501	118,203	105,975
Occupancy expense	111,179	109,169	104,690
Equipment expense	112,290	102,909	97,478
Processing fees paid to third parties	29,552	30,017	25,673
FDIC insurance expense	10,664	18,890	22,191
Collection and foreclosure-related expenses	11,994	16,567	14,407
Merger-related expenses	17,166	6,462	9,015
Other	139,283	147,063	142,430
Total noninterest expense	1,103,741	1,076,971	1,012,469
Income before income taxes	592,048	503,610	543,698
Income taxes	134,677	103,297	219,946
Net income	$ 457,371	$ 400,313	$ 323,752
Average shares outstanding (in shares)	11,141,069	11,938,439	12,010,405
Net income per share	$ 41.05	$ 33.53	$ 29.96
Cash dividends (in dollars per share)	$ 1.60	$ 1.45	$ 1.25
Service charges on deposit accounts
Noninterest income
Revenue from contracts with customers	$ 105,191	$ 105,486	$ 101,201
Wealth management services
Noninterest income
Revenue from contracts with customers	99,241	97,966	86,719
Cardholder services, net
Noninterest income
Revenue from contracts with customers	69,078	65,478	57,583
Other service charges and fees
Noninterest income
Revenue from contracts with customers	31,644	30,606	28,321
Mortgage income
Noninterest income
Revenue from contracts with customers	24,304	24,504	22,678
Insurance commissions
Noninterest income
Revenue from contracts with customers	12,810	12,702	12,465
ATM income
Noninterest income
Revenue from contracts with customers	$ 6,296	$ 7,980	$ 9,143