Consolidated Statements of Income - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Interest income:
Interest and fees on loans	$ 96.5	$ 73.9	$ 188.2	$ 137.6
Interest and dividends on investment securities:
Taxable	13.9	9.8	27.1	18.5
Exempt from federal taxes	0.6	0.9	1.2	1.7
Interest on deposits in banks	2.0	1.3	4.1	2.5
Total interest income	113.0	85.9	220.6	160.3
Interest expense:
Interest on deposits	7.2	5.0	13.4	9.1
Interest on securities sold under repurchase agreements	0.7	0.3	1.1	0.5
Interest on other borrowed funds	0.0	0.0	0.1	0.0
Interest on other debt	0.3	0.5	0.5	1.0
Interest on subordinated debentures held by subsidiary trusts	1.0	0.8	1.9	1.5
Total interest expense	9.2	6.6	17.0	12.1
Net interest income	103.8	79.3	203.6	148.2
Provision for loan losses	2.9	2.4	5.0	4.1
Net interest income after provision for loan losses	100.9	76.9	198.6	144.1
Non-interest income:
Mortgage banking revenues	7.2	7.6	12.6	14.1
Investment securities gains (losses), net	0.0	0.0	0.0	0.0
Other income	2.6	5.8	6.5	7.9
Total non-interest income	37.6	37.2	72.8	66.3
Non-interest expense:
Salaries and wages	34.3	28.0	68.9	53.7
Employee benefits	12.3	9.8	23.6	19.4
Outsourced technology services	7.1	6.0	14.1	11.3
Occupancy, net	6.0	5.2	12.3	10.0
Furniture and equipment	2.9	2.8	6.0	5.1
OREO expense, net of income	(0.1)	0.0	0.1	0.0
Professional fees	2.1	1.8	3.3	2.8
FDIC insurance premiums	1.4	0.8	2.9	1.7
Mortgage servicing rights amortization	0.7	0.7	1.5	1.3
Mortgage servicing rights recovery	0.0	0.0	0.0	(0.1)
Core deposit intangibles amortization	1.7	1.1	3.5	1.7
Other expenses	16.5	14.1	32.3	26.4
Acquisition related expenses	0.0	10.1	2.3	10.8
Total non-interest expense	84.9	80.4	170.8	144.1
Income before income tax expense	53.6	33.7	100.6	66.3
Income tax expense	11.9	11.9	22.2	21.3
Net income	$ 41.7	$ 21.8	$ 78.4	$ 45.0
Basic earnings per common share (in dollars per share)	$ 0.74	$ 0.46	$ 1.39	$ 0.97
Diluted earnings per common share (in dollars per share)	$ 0.74	$ 0.45	$ 1.38	$ 0.96
Weighted average common shares outstanding for basic earnings per share computation	56,335,186	47,612,971	56,288,453	46,170,500
Weighted Average Number of Shares Outstanding, Diluted	56,699,021	48,074,451	56,670,400	46,681,375
Credit and Debit Card [Member]
Non-interest income:
Payment services revenues	$ 12.9	$ 10.2	$ 23.4	$ 18.6
Investment Advisory, Management and Administrative Service [Member]
Non-interest income:
Wealth management revenues	5.8	5.1	11.7	10.1
Deposit Account [Member]
Non-interest income:
Payment services revenues	5.3	5.1	10.9	9.5
Financial Service, Other [Member]
Non-interest income:
Payment services revenues	$ 3.8	$ 3.4	$ 7.7	$ 6.1