Consolidated Statements of Cash Flows - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash flows from operating activities:
Net income	$ 114.3	$ 128.6
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for credit losses	53.7	10.1
Net loss on disposal of premises and equipment	0.1	0.0
Depreciation and amortization	33.0	29.0
Net premium amortization on investment securities	10.2	6.4
Debt and Equity Securities, Gain (Loss)	(0.1)	(0.1)
Realized and unrealized net gains on mortgage banking activities	(39.3)	(21.1)
Net gain on sale of investments in unrelated entities	(1.0)	0.0
Net gain on sale of OREO	(0.7)	(1.7)
Write-downs of OREO and other assets pending disposal	0.1	0.7
Mortgage servicing rights impairment	9.9	0.0
Deferred taxes	7.1	(0.5)
Net increase in cash surrender value of company-owned life insurance	(5.6)	(4.2)
Stock-based compensation expense	5.6	6.6
Originations of mortgage loans held for sale	(1,148.7)	(770.1)
Proceeds from sales of mortgage loans held for sale	1,177.2	710.9
Changes in operating assets and liabilities, net of effects of acquisition:
Increase in interest receivable	(10.0)	(4.0)
Increase in other assets	(40.3)	(31.0)
Decrease in accrued interest payable	(4.0)	(13.6)
Increase in accounts payable and accrued expenses	15.5	9.7
Net cash provided by operating activities	162.8	56.7
Purchases of investment securities:
Available-for-sale	(1,548.8)	(740.3)
Proceeds from maturities and pay-downs of investment securities:
Held-to-maturity	37.2	33.2
Available-for-sale	1,114.9	681.9
Proceeds from Life Insurance Policy	4.4	1.6
Extensions of credit to clients, net of repayments	(1,240.0)	(136.0)
Recoveries of loans charged-off	5.1	8.2
Proceeds from sale of OREO	6.6	14.0
Proceeds from the sale of Health Savings Accounts	0.0	0.3
Proceeds from sale of investments in unrelated entities	2.2	0.0
Acquisition of bank and bank holding company, net of cash and cash equivalents received	0.0	298.4
Capital expenditures, net of sales	(17.7)	(10.2)
Net cash (used in) provided by investing activities	(1,636.1)	151.1
Cash flows from financing activities:
Net increase in deposits	2,218.9	412.3
Net increase (decrease) in securities sold under repurchase agreements	122.7	(105.9)
Net decrease in other borrowed funds	0.0	(4.1)
Repayments of long-term debt	(0.1)	(2.0)
Advances on long-term debt	98.6	0.1
Proceeds from issuance of common stock	0.8	0.9
Purchase and retirement of common stock	(78.9)	(2.5)
Dividends paid to common stockholders	(104.9)	(59.0)
Net cash provided by financing activities	2,257.1	239.8
Net increase in cash and cash equivalents	783.8	447.6
Cash and cash equivalents at beginning of period	1,076.8	822.0
Cash and cash equivalents at end of period	1,860.6	1,269.6
Supplemental disclosures of cash flow information:
Cash paid during the period for income taxes	36.0	34.8
Cash paid during the period for interest expense	25.4	42.7
Supplemental disclosures of non-cash investing and financing activities:
Right-of-use assets obtained in exchange for operating lease liabilities	3.5	39.6
Transfer of loans to other real estate owned	3.2	14.0
Capitalization of internally originated mortgage servicing rights	9.5	2.8
Supplemental schedule of noncash investing activities from acquisitions:
Investment securities available for sale	0.0	78.7
Loans held for sale	0.0	0.5
Loans held for investment	0.0	416.6
Premises and equipment	0.0	23.6
Goodwill	0.0	76.3
Core deposit intangible	0.0	16.6
Company-owned life insurance	0.0	15.2
Interest receivable	0.0	2.2
Other real estate owned	0.0	2.4
Other assets	0.0	6.5
Total noncash assets acquired	0.0	638.6
Deposits	0.0	706.7
Securities sold under repurchase agreements	0.0	30.4
Accounts payable and accrued expenses	0.0	19.4
Deferred tax liability	0.0	0.4
Total liabilities assumed	0.0	760.2
Other Borrowings	$ 0.0	$ 4.1