Income Taxes - Uncertain Tax Positions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Uncertain tax positions:
Beginning of year	$ 6.4	$ 6.9	$ 7.2
Increases related to prior-year tax positions	0.1	0.6	0.0
Decreases related to prior-year tax positions	(0.5)	(0.4)	(0.3)
Increases related to current-year tax positions	1.4	1.2	1.1
Increases related to acquisitions	4.2	0.0	0.0
Settlements	(0.1)	(0.8)	0.0
Effect of the expiration of statutes of limitation	(0.8)	(0.8)	(0.7)
Foreign currency exchange effects	(0.3)	(0.3)	(0.4)
End of year	$ 10.4	$ 6.4	$ 6.9