Consolidated Statements of Income - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Interest income
Loans and leases	$ 315,012,000	$ 272,215,000	$ 909,167,000	$ 785,283,000
Investment securities and dividend income	40,155,000	38,770,000	119,976,000	110,969,000
Overnight investments	7,151,000	4,721,000	20,820,000	15,932,000
Total interest income	362,318,000	315,706,000	1,049,963,000	912,184,000
Interest expense
Deposits	21,737,000	5,147,000	53,821,000	13,424,000
Short-term borrowings	542,000	398,000	1,516,000	1,175,000
Federal Home Loan Bank borrowings	1,316,000	1,099,000	4,187,000	4,335,000
Subordinated debentures	1,774,000	1,561,000	5,398,000	4,655,000
Long-term obligations	524,000	139,000	796,000	577,000
Total interest expense	25,893,000	8,344,000	65,718,000	24,166,000
Net interest income	336,425,000	307,362,000	984,245,000	888,018,000
Provision (credit) for loan and lease losses	6,766,000	840,000	23,714,000	16,883,000
Net interest income after provision for loan and lease losses	329,659,000	306,522,000	960,531,000	871,135,000
Noninterest income
Debt and Equity Securities, Gain (Loss)	1,136,000	0	6,855,000	0
Marketable equity securities (losses) gains, net	(967,000)	3,854,000	13,505,000	9,265,000
Gain on extinguishment of debt	0	703,000	0	26,517,000
Other	6,176,000	2,538,000	15,129,000	15,703,000
Total noninterest income	100,930,000	94,531,000	311,468,000	318,142,000
Noninterest expense
Salaries and wages	137,841,000	133,867,000	406,788,000	392,911,000
Employee benefits	28,358,000	28,850,000	91,090,000	90,656,000
Occupancy expense	28,163,000	26,632,000	82,810,000	80,686,000
Equipment expense	28,770,000	25,880,000	83,999,000	76,021,000
Processing fees paid to third parties	7,250,000	7,297,000	20,980,000	23,383,000
FDIC insurance expense	2,440,000	5,186,000	7,857,000	16,411,000
Collection and foreclosure-related expenses	3,044,000	4,269,000	9,725,000	12,389,000
Merger-related expenses	3,892,000	1,126,000	9,695,000	4,136,000
Other	30,667,000	34,430,000	98,535,000	105,000,000
Total noninterest expense	270,425,000	267,537,000	811,479,000	801,593,000
Income before income taxes	160,164,000	133,516,000	460,520,000	387,684,000
Income taxes	35,385,000	16,198,000	105,023,000	76,844,000
Net income	$ 124,779,000	$ 117,318,000	$ 355,497,000	$ 310,840,000
Average shares outstanding (in shares)	11,060,462	11,971,460	11,286,984	11,997,281
Net income per share	$ 11.27	$ 9.80	$ 31.50	$ 25.91
Cardholder services, net
Noninterest income
Revenue from contract with customers	$ 15,957,000	$ 14,678,000	$ 51,069,000	$ 44,385,000
Merchant services, net
Noninterest income
Revenue from contract with customers	6,034,000	5,857,000	18,324,000	18,512,000
Service charges on deposit accounts
Noninterest income
Revenue from contract with customers	27,112,000	25,994,000	77,967,000	78,489,000
Wealth management services
Noninterest income
Revenue from contract with customers	25,212,000	24,459,000	74,786,000	73,543,000
Other service charges and fees
Noninterest income
Revenue from contract with customers	8,237,000	7,651,000	23,823,000	22,887,000
Mortgage income
Noninterest income
Revenue from contract with customers	7,438,000	4,123,000	16,134,000	13,063,000
Insurance commissions
Noninterest income
Revenue from contract with customers	2,960,000	2,755,000	9,105,000	9,471,000
ATM income
Noninterest income
Revenue from contract with customers	$ 1,635,000	$ 1,919,000	$ 4,771,000	$ 6,307,000