Derivatives and Hedging Activities - Schedule of Notional Amounts of Outstanding Derivative Positions (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Derivative Asset, Notional Amount	$ 526.1	$ 454.3
Derivative Asset, Estimated Fair Value	14.6	10.1
Notional amount of terminated commitment	539.6	467.9
Derivative Liabilities, Estimated Fair Value	13.5	9.4
Not Designated as Hedging Instrument | Interest rate swap contracts
Derivative [Line Items]
Derivative Asset, Notional Amount	449.2	403.3
Derivative Asset, Estimated Fair Value	12.7	8.8
Notional amount of terminated commitment	449.2	403.3
Derivative Liabilities, Estimated Fair Value	12.7	8.8
Not Designated as Hedging Instrument | Interest rate lock commitments
Derivative [Line Items]
Derivative Asset, Notional Amount	76.9	51.0
Derivative Asset, Estimated Fair Value	1.9	1.3
Not Designated as Hedging Instrument | Forward loan sales contracts
Derivative [Line Items]
Notional amount of terminated commitment	90.4	64.6
Derivative Liabilities, Estimated Fair Value	$ 0.8	$ 0.6