Consolidated Statements of Cash Flows - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash flows from operating activities:
Net income	$ 128.6	$ 119.8
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for loan losses	10.1	7.0
Depreciation and amortization	29.0	19.9
Net premium amortization on investment securities	6.4	7.9
Net gain on investment securities transactions	(0.1)	0.0
Realized and unrealized net gains on mortgage banking activities	(21.1)	(4.2)
Net loss (gain) on sale of OREO	(1.7)	(0.4)
Write-downs of OREO and other assets pending disposal	0.7	0.1
Deferred income tax expense	0.5	13.2
Net increase in cash surrender value of company-owned life insurance	(4.2)	(3.6)
Stock-based compensation expense	6.6	4.3
Originations of mortgage loans held for sale	(770.1)	(738.3)
Proceeds from sales of mortgage loans held for sale	710.9	747.1
Changes in operating assets and liabilities, net of effects of acquisition:
Increase in interest receivable	(4.0)	(6.4)
Increase in other assets	(31.0)	(0.7)
(Decrease) increase in accrued interest payable	(13.6)	0.9
Decrease in accounts payable and accrued expenses	9.7	5.3
Net cash provided by operating activities	56.7	171.9
Purchases of investment securities:
Held-to-maturity	0.0	(0.3)
Available-for-sale	(740.3)	(320.6)
Proceeds from maturities and pay-downs of investment securities:
Held-to-maturity	33.2	66.9
Available-for-sale	681.9	333.3
Purchases of company-owned life insurance	1.6	0.0
Extensions of credit to customers, net of repayments	(136.0)	(225.5)
Recoveries of loans charged-off	8.2	9.6
Proceeds from sale of OREO	14.0	4.3
Proceeds from the sale of Health Savings Accounts	0.3	0.0
Acquisition of bank and bank holding company, net of cash and cash equivalents received	298.4	28.2
Capital expenditures, net of sales	(10.2)	(0.5)
Net cash provided by (used in) investing activities	151.1	(104.6)
Cash flows from financing activities:
Net increase in deposits	412.3	214.4
Net decrease in securities sold under repurchase agreements	(105.9)	(7.1)
Net decrease in other borrowed funds	(4.1)	(24.5)
Repayments of long-term debt	(2.0)	(0.4)
Advances on long-term debt	0.1	2.7
Proceeds from issuance of common stock	0.9	1.9
Purchase and retirement of common stock	(2.5)	(1.0)
Dividends paid to common stockholders	(59.0)	(47.2)
Net cash provided by financing activities	239.8	138.8
Net increase in cash and cash equivalents	447.6	206.1
Cash and cash equivalents at beginning of period	822.0	758.9
Cash and cash equivalents at end of period	1,269.6	965.0
Supplemental disclosures of cash flow information:
Cash paid during the period for income taxes	34.8	15.8
Cash paid during the period for interest expense	42.7	27.1
Supplemental disclosures of non-cash investing and financing activities:
Amortization of unrealized gains and losses on transfers of securities	0.0	1.4
Right-of-use assets obtained in exchange for operating lease liabilities	39.6	0.0
Transfer of loans to other real estate owned	14.0	10.7
Capitalization of internally originated mortgage servicing rights	2.8	4.5
Supplemental schedule of noncash investing activities from acquisitions:
Investment securities available for sale	78.7	3.1
Loans held for sale	0.5	0.0
Loans	416.6	713.1
Premises and equipment	23.6	14.0
Goodwill	76.3	100.8
Core deposit intangible	16.6	15.7
Company-owned life insurance	15.2	9.5
Interest receivable	2.2	3.6
Other real estate owned	2.4	0.6
Other assets	6.5	6.5
Total noncash assets acquired	638.6	866.9
Liabilities assumed:
Deposits	706.7	696.3
Securities sold under repurchase agreements	30.4	0.0
Accounts payable and accrued expenses	19.4	7.7
Long-term debt	0.0	7.0
Other borrowed funds	4.1	6.0
Trust preferred securities	0.0	4.4
Deferred tax liability	(0.4)	0.4
Total liabilities assumed	$ 760.2	$ 721.8