Derivatives and Hedging Activities - Notional Amounts and Estimated Fair Values of Derivatives (Details) $ in Millions	Dec. 31, 2020 USD ($)	May 01, 2020 USD ($)	Dec. 31, 2019 USD ($)
Derivative [Line Items]
Derivative Asset, Notional Amount	$ 901.6		$ 571.0
Derivative Assets, Estimated Fair Value	55.3		23.2
Derivative Liability, Notional Amount	1,014.1		631.2
Derivative Liabilities, Estimated Fair Value	53.3		22.2
Interest Rate Cash Flow Hedge Derivative at Fair Value, Net	0.0
Interest Rate Swap
Derivative [Line Items]
Derivative Liability, Notional Amount		$ 46.4
Derivative, Notional Amount, Contract 2		36.1
Derivative, Notional Amount, Contract 3		$ 5.1
Derivative, Fixed Interest Rate, Contract 1		0.0040
Derivative, Fixed Interest Rate, Contract 2		0.0034
Derivative, Fixed Interest Rate, Contract 3		0.0040
Not Designated as Hedging Instrument | Interest Rate Swap
Derivative [Line Items]
Derivative Asset, Notional Amount	799.7		503.2
Derivative Assets, Estimated Fair Value	52.0		21.9
Derivative Liability, Notional Amount	799.7		503.2
Derivative Liabilities, Estimated Fair Value	52.0		21.9
Not Designated as Hedging Instrument | Interest rate lock commitments
Derivative [Line Items]
Derivative Asset, Notional Amount	101.9		67.8
Derivative Assets, Estimated Fair Value	3.3		1.3
Not Designated as Hedging Instrument | Forward loan sales contracts
Derivative [Line Items]
Derivative Liability, Notional Amount	126.8		128.0
Derivative Liabilities, Estimated Fair Value	1.1		0.3
Designated as Hedging Instrument | Interest Rate Swap
Derivative [Line Items]
Derivative Asset, Notional Amount	87.6		0.0
Derivative Assets, Estimated Fair Value	$ 0.2		$ 0.0