Goodwill and Other Intangible Assets - Intangible Assets and Amortization Expense (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Finite-Lived Intangible Assets
Gross carrying amount	$ 56.5		$ 56.5		$ 46.8
Accumulated amortization	28.5		28.5		25.3
Intangible assets, net	60.0		60.0		53.5
Amortization expense	1.6	$ 1.9	3.2	$ 4.6
Q3 - Q4 2018	3.3		3.3
2019	6.4		6.4
2020	6.3		6.3
2021	6.3		6.3
2022	1.1		1.1
Trademarks
Finite-Lived Intangible Assets
Unamortized intangible assets, gross carrying amount	32.0		32.0		32.0
Trademarks
Finite-Lived Intangible Assets
Gross carrying amount	0.5		0.5		0.3
Accumulated amortization	0.2		0.2		0.2
Patents
Finite-Lived Intangible Assets
Gross carrying amount	40.8		40.8		40.8
Accumulated amortization	24.5		24.5		22.2
Customer relationships
Finite-Lived Intangible Assets
Gross carrying amount	10.6		10.6		3.3
Accumulated amortization	1.3		1.3		0.7
Unpatented technologies
Finite-Lived Intangible Assets
Gross carrying amount	4.4		4.4		2.4
Accumulated amortization	2.5		2.5		2.2
Other
Finite-Lived Intangible Assets
Gross carrying amount	0.2		0.2		0.0
Accumulated amortization	$ 0.0		$ 0.0		$ 0.0