Derivatives and Hedging Activities - Schedule of Notional Amounts of Outstanding Derivative Positions (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Derivative Assets (included in other assets on the consolidated balance sheets):
Derivative Asset, Notional Amount	$ 578.6	$ 454.3
Derivative Asset, Estimated Fair Value	24.5	10.1
Derivative Liabilities (included in accounts payable and accrued expenses on the consolidated balance sheets):
Derivative Liabilities, Notional Amount	597.2	467.9
Derivative Liabilities, Estimated Fair Value	22.7	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	465.9	403.3
Derivative Asset, Estimated Fair Value	22.0	8.8
Derivative Liabilities (included in accounts payable and accrued expenses on the consolidated balance sheets):
Derivative Liabilities, Notional Amount	465.9	403.3
Derivative Liabilities, Estimated Fair Value	22.0	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	112.7	51.0
Derivative Asset, Estimated Fair Value	2.5	1.3
Not Designated as Hedging Instrument | Forward loan sales contracts
Derivative Liabilities (included in accounts payable and accrued expenses on the consolidated balance sheets):
Derivative Liabilities, Notional Amount	131.3	64.6
Derivative Liabilities, Estimated Fair Value	$ 0.7	$ 0.6