Derivatives and Hedging Activities - Schedule of Notional Amounts of Outstanding Derivative Positions (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Derivative Assets (included in other assets on the consolidated balance sheets):
Derivative Asset, Notional Amount	$ 791.1	$ 454.3
Derivative Asset, Estimated Fair Value	33.0	10.1
Derivative Liabilities (included in accounts payable and accrued expenses on the consolidated balance sheets):
Derivative Liabilities, Notional Amount	494.0	467.9
Derivative Liabilities, Estimated Fair Value	30.8	9.4
Not Designated as Hedging Instrument | Interest rate swap contracts
Derivative Assets (included in other assets on the consolidated balance sheets):
Derivative Asset, Notional Amount	494.0	403.3
Derivative Asset, Estimated Fair Value	30.8	8.8
Derivative Liabilities (included in accounts payable and accrued expenses on the consolidated balance sheets):
Derivative Liabilities, Notional Amount	494.0	403.3
Derivative Liabilities, Estimated Fair Value	30.8	8.8
Not Designated as Hedging Instrument | Interest rate lock commitments
Derivative Assets (included in other assets on the consolidated balance sheets):
Derivative Asset, Notional Amount	122.4	51.0
Derivative Asset, Estimated Fair Value	2.0	1.3
Not Designated as Hedging Instrument | Forward loan sales contracts
Derivative Assets (included in other assets on the consolidated balance sheets):
Derivative Asset, Notional Amount	174.7	0.0
Derivative Asset, Estimated Fair Value	0.2	0.0
Derivative Liabilities (included in accounts payable and accrued expenses on the consolidated balance sheets):
Derivative Liabilities, Notional Amount	0.0	64.6
Derivative Liabilities, Estimated Fair Value	$ 0.0	$ 0.6