Derivatives and Hedging Activities - Notional Amounts and Estimated Fair Values of Derivatives (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Derivative Asset, Notional Amount	$ 571.0	$ 454.3
Derivative Assets, Estimated Fair Value	23.2	10.1
Derivative Liability, Notional Amount	631.2	467.9
Derivative Liabilities, Estimated Fair Value	22.2	9.4
Not Designated as Hedging Instrument | Interest rate swap contracts
Derivative [Line Items]
Derivative Asset, Notional Amount	503.2	403.3
Derivative Assets, Estimated Fair Value	21.9	8.8
Derivative Liability, Notional Amount	503.2	403.3
Derivative Liabilities, Estimated Fair Value	21.9	8.8
Not Designated as Hedging Instrument | Interest rate lock commitments
Derivative [Line Items]
Derivative Asset, Notional Amount	67.8	51.0
Derivative Assets, Estimated Fair Value	1.3	1.3
Not Designated as Hedging Instrument | Forward loan sales contracts
Derivative [Line Items]
Derivative Liability, Notional Amount	128.0	64.6
Derivative Liabilities, Estimated Fair Value	$ 0.3	$ 0.6