Loans - Schedule of Changes in the Accretable Yield for Loans Acquired (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Receivables [Abstract]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield, Acquired	$ 3.2	$ 0.0	$ 3.2	$ 0.0
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield, Additions	0.0	0.2	0.4	2.1
Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Beginning Balance	6.5	7.7	7.3	6.8
Accretion income	(0.7)	(0.9)	(2.4)	(2.1)
Reductions due to exit events	(0.1)	(0.1)	(0.6)	(1.1)
Reclassifications from nonaccretable differences	0.6	0.5	1.6	1.7
Ending Balance	9.5	7.4	9.5	7.4
Interest Income on Non-Accrual Loans if Accrued	$ 0.8	$ 0.9	$ 1.6	$ 1.8