Derivatives and Hedging Activities - Schedule of Notional Amounts of Outstanding Derivative Positions (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Derivative [Line Items]
Derivative liability, Fair Value of Financial Collateral in the Balance Sheet	$ 7.4	$ 3.3
Derivative Asset, Notional Amount	463.5	404.9
Derivative Asset, Estimated Fair Value	11.8	8.8
Notional amount of terminated commitment	492.1	433.0
Derivative Liabilities, Estimated Fair Value	9.7	7.9
Interest rate swap contracts
Derivative [Line Items]
Derivative liability, Fair Value of Financial Collateral in the Balance Sheet	7.4	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	389.8	344.2
Derivative Asset, Estimated Fair Value	10.1	7.5
Notional amount of terminated commitment	389.8	344.2
Derivative Liabilities, Estimated Fair Value	9.3	7.8
Not Designated as Hedging Instrument \| Interest rate lock commitments
Derivative [Line Items]
Derivative Asset, Notional Amount	73.7	60.7
Derivative Asset, Estimated Fair Value	1.7	1.3
Not Designated as Hedging Instrument \| Forward loan sales contracts
Derivative [Line Items]
Notional amount of terminated commitment	102.3	88.8
Derivative Liabilities, Estimated Fair Value	$ 0.4	$ 0.1

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

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Amount of right to receive cash collateral under master netting arrangements that have not been offset against derivative liabilities.

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