Consolidated Statements of Income - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Interest income:
Interest and fees on loans	$ 111.4	$ 91.7
Interest and dividends on investment securities:
Taxable	15.1	13.2
Exempt from federal taxes	0.5	0.6
Interest on deposits in banks	3.6	2.1
Total interest income	130.6	107.6
Interest expense:
Interest on deposits	12.1	6.2
Interest on securities sold under repurchase agreements	1.0	0.4
Interest on other borrowed funds	0.0	0.1
Interest on other debt	0.3	0.2
Interest on subordinated debentures held by subsidiary trusts	1.2	0.9
Total interest expense	14.6	7.8
Net interest income	116.0	99.8
Provision for loan losses	3.7	2.1
Net interest income after provision for loan losses	112.3	97.7
Non-interest income:
Mortgage banking revenues	5.4	5.4
Investment securities gains (losses), net	0.0	0.0
Other income	4.3	3.9
Total non-interest income	34.5	35.2
Non-interest expense:
Salaries and wages	36.1	34.6
Employee benefits	14.4	11.3
Outsourced technology services	7.9	7.0
Occupancy, net	7.0	6.3
Furniture and equipment	3.5	3.1
OREO expense, net of income	0.1	0.2
Professional fees	1.9	1.2
FDIC insurance premiums	1.5	1.5
Mortgage servicing rights amortization	0.9	0.8
Core deposit intangibles amortization	2.3	1.8
Other expenses	15.9	15.8
Acquisition related expenses	2.3	2.3
Total non-interest expense	93.8	85.9
Income before income tax expense	53.0	47.0
Income tax expense	11.4	10.3
Net income	$ 41.6	$ 36.7
Basic earnings per common share (in dollars per share)	$ 0.69	$ 0.65
Diluted earnings per common share (in dollars per share)	$ 0.69	$ 0.65
Weighted average common shares outstanding for basic earnings per share computation	60,311,171	56,241,201
Weighted Average Number of Shares Outstanding, Diluted	60,598,070	56,652,178
Credit and Debit Card [Member]
Non-interest income:
Payment services revenues	$ 9.4	$ 10.5
Investment Advisory, Management and Administrative Service [Member]
Non-interest income:
Wealth management revenues	6.1	5.9
Deposit Account [Member]
Non-interest income:
Payment services revenues	5.0	5.6
Financial Service, Other [Member]
Non-interest income:
Payment services revenues	$ 4.3	$ 3.9