Derivatives and Hedging Activities - Schedule of Notional Amounts of Outstanding Derivative Positions (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Derivative [Line Items]
Derivative liability, Fair Value of Financial Collateral in the Balance Sheet	$ 10.0	$ 3.3
Derivative Asset, Notional Amount	449.7	404.9
Derivative Asset, Estimated Fair Value	12.4	8.8
Notional amount of terminated commitment	464.2	433.0
Derivative Liabilities, Estimated Fair Value	11.3	7.9
Interest rate swap contracts
Derivative [Line Items]
Derivative liability, Fair Value of Financial Collateral in the Balance Sheet	10.0	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	386.8	344.2
Derivative Asset, Estimated Fair Value	11.3	7.5
Notional amount of terminated commitment	386.8	344.2
Derivative Liabilities, Estimated Fair Value	11.1	7.8
Not Designated as Hedging Instrument \| Interest rate lock commitments
Derivative [Line Items]
Derivative Asset, Notional Amount	62.9	60.7
Derivative Asset, Estimated Fair Value	1.1	1.3
Not Designated as Hedging Instrument \| Forward loan sales contracts
Derivative [Line Items]
Notional amount of terminated commitment	77.4	88.8
Derivative Liabilities, Estimated Fair Value	$ 0.2	$ 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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