Derivatives and Hedging Activities - Schedule of Notional Amounts of Outstanding Derivative Positions (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Derivative liability, Fair Value of Financial Collateral in the Balance Sheet	$ 5.7	$ 3.3
Derivative Asset, Notional Amount	437.4	404.9
Derivative Asset, Estimated Fair Value	9.7	8.8
Notional amount of terminated commitment	466.2	433.0
Derivative Liabilities, Estimated Fair Value	7.9	7.9
Interest rate swap contracts
Derivative [Line Items]
Derivative liability, Fair Value of Financial Collateral in the Balance Sheet	5.7	3.3
Mortgage Related Derivatives
Derivative [Line Items]
Derivative liability, Fair Value of Financial Collateral in the Balance Sheet	0.0	0.0
Not Designated as Hedging Instrument \| Interest rate swap contracts
Derivative [Line Items]
Derivative Asset, Notional Amount	370.5	344.2
Derivative Asset, Estimated Fair Value	8.3	7.5
Notional amount of terminated commitment	370.5	344.2
Derivative Liabilities, Estimated Fair Value	7.7	7.8
Not Designated as Hedging Instrument \| Interest rate lock commitments
Derivative [Line Items]
Derivative Asset, Notional Amount	66.9	60.7
Derivative Asset, Estimated Fair Value	1.4	1.3
Not Designated as Hedging Instrument \| Forward loan sales contracts
Derivative [Line Items]
Notional amount of terminated commitment	95.7	88.8
Derivative Liabilities, Estimated Fair Value	$ 0.2	$ 0.1

Nominal or face amount used to calculate payments on the derivative asset.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5579245-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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Amount of right to receive cash collateral under master netting arrangements that have not been offset against derivative liabilities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 55
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Nominal or face amount used to calculate payments on the derivative liability.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Fair value as of the balance sheet date of interest rate derivative assets, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized as assets.

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Fair value as of the balance sheet date of interest rate derivative liabilities, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized as liabilities.

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