Derivatives and Hedging Activities - Schedule of Derivative Instruments, Effect on Other Comprehensive Income (Loss) (Details) - Not Designated as Hedging Instrument - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Derivative [Line Items]
Amount of gain recognized in other non-interest income	$ 0.3	$ 0.0
Amount of net fee income recognized in other non-interest income	0.5	0.0
Amount of net gains recognized in mortgage banking revenues	$ (0.1)	$ (0.1)