Retirement Plans - Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Settlements and curtailments	$ 1.4	$ 2.6
United States
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Interest cost	2.5	2.9
Expected return on plan assets	(3.3)	(3.8)
Amortization of net actuarial loss	0.3	0.4
Net periodic pension cost (credit)	(0.5)	(0.5)
Settlements and curtailments	1.1	2.9
Total pension cost	0.6	2.4
Germany
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Interest cost	0.4	0.6
Expected return on plan assets	(0.6)	(0.6)
Amortization of net actuarial loss	0.4	0.2
Net periodic pension cost (credit)	0.2	0.2
Settlements and curtailments		0.0
Total pension cost	$ 0.2	$ 0.2