Income Taxes - Unrecognized Income Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Unrecognized Tax Benefits
Unrecognized tax benefits at beginning of the year	$ 0.8	$ 0.8	$ 1.0
Additions for tax positions of prior years	0.9	0.1	0.0
Additions for tax positions acquired	1.4	0.0	0.0
Reductions for tax positions of prior years	(0.8)	(0.1)	0.0
Lapse of statutes of limitation	0.0	0.0	(0.2)
Unrecognized tax benefits at end of the year	$ 2.3	$ 0.8	$ 0.8