Consolidated Statements of Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Interest income:
Interest and fees on loans	$ 935.6	$ 1,022.2	$ 979.7
Interest and dividends on investment securities:
Taxable	199.4	243.5	269.1
Exempt from federal taxes	2.9	2.8	3.2
Interest on deposits in banks	32.7	22.2	15.7
Total interest income	1,178.0	1,302.5	1,280.1
Interest expense:
Interest on deposits	299.8	325.9	242.6
Interest on securities sold under repurchase agreements	4.7	6.7	6.4
Interest on other borrowed funds	26.2	123.4	133.8
Interest on long-term debt	10.7	11.8	5.8
Interest on subordinated debentures held by subsidiary trusts	11.2	13.1	12.7
Total interest expense	352.6	480.9	401.3
Net interest income	825.4	821.6	878.8
Provision for credit losses	26.8	67.8	32.2
Net interest income after provision for credit losses	798.6	753.8	846.6
Payment Services Revenues	67.9	73.6	76.4
Noninterest income:
Revenue from Contract with Customer, Excluding Assessed Tax	8.8	9.0	9.5
Fees and Commissions, Mortgage Banking and Servicing	5.8	6.6	8.4
Investment Banking, Advisory, Brokerage, and Underwriting Fees and Commissions	40.6	38.8	35.3
Service Charges on Deposit Accounts	27.0	25.7	23.0
Investment securities losses, net	0.0	0.0	(23.5)
Other income	83.3	24.4	17.9
Total noninterest income	233.4	178.1	147.0
Noninterest expense:
Salaries and wages	274.6	270.9	263.1
Employee benefits	74.6	76.4	75.3
Information Technology and Data Processing	57.5	56.2	59.0
Occupancy, Net	54.8	48.7	48.0
Equipment Expense	20.6	20.7	22.1
OREO expense, net	0.5	4.1	1.5
Professional fees	23.7	21.6	19.1
FDIC insurance premiums	14.4	24.0	31.5
Other intangibles amortization	13.6	14.6	15.7
Other expenses	106.0	100.2	121.5
Total noninterest expense	640.3	637.4	656.8
Income before income tax	391.7	294.5	336.8
Provision for income tax	89.6	68.5	79.3
Net income	$ 302.1	$ 226.0	$ 257.5
Basic earnings per common share (in dollars per share)	$ 2.95	$ 2.19	$ 2.48
Diluted earnings per common share (in dollars per share)	$ 2.94	$ 2.19	$ 2.48
Other Interest and Dividend Income	$ 7.4	$ 11.8	$ 12.4