Derivatives and Hedging Activities - Schedule of Derivative Instruments, Effect on Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Derivative [Line Items]
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, before Tax	$ 0.0	$ (0.6)	$ 0.0	$ (1.1)
Designated as Hedging Instrument [Member]
Derivative [Line Items]
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, before Tax	0.0	0.7	0.0	1.1
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	0.0	(1.1)	0.0	(1.1)
Not Designated as Hedging Instrument
Derivative [Line Items]
Amount of gain recognized in other non-interest income	0.1	0.0	0.4	0.0
Amount of net fee income recognized in other non-interest income	0.0	0.2	0.9	0.4
Amount of net gains recognized in mortgage banking revenues	$ 0.0	$ 0.4	$ 0.0	$ 0.5