Other Real Estate Owned (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Real Estate Acquired Through Foreclosure [Roll Forward]
Balance at beginning of year	$ 10.1	$ 10.0	$ 6.3
Acquisitions	0.6	1.2	1.1
Additions	12.1	5.4	7.6
Valuation adjustments	(0.1)	(0.4)	(0.6)
Dispositions	(8.3)	(6.1)	(4.4)
Balance at end of year	14.4	10.1	10.0
Write-downs of OREO	$ (0.1)	$ (0.4)	$ (0.6)