Property, Plant and Equipment, net (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment
Construction in Progress Expenditures Incurred but Not yet Paid			$ 3.8	$ 3.1	$ 5.9	$ 4.1
Document Period End Date			Sep. 30, 2017
Gross property, plant and equipment	$ 616.3		$ 616.3		602.3
Less: Accumulated depreciation and amortization	328.6		328.6		301.0
Net property, plant and equipment	287.7		287.7		301.3
Loss on disposal of property, plant and equipment	0.0	$ 0.1	0.0	0.1
Net capitalized turnaround costs:
Beginning balance			26.6	37.8	37.8
Additions			1.9	3.5
Depreciation			(11.7)	(11.6)
Ending balance	16.8	$ 29.7	16.8	$ 29.7	26.6	$ 37.8
Land
Property, Plant and Equipment
Gross property, plant and equipment	1.4		1.4		1.4
Buildings and improvements
Property, Plant and Equipment
Gross property, plant and equipment	16.9		16.9		16.7
Machinery and equipment
Property, Plant and Equipment
Gross property, plant and equipment	566.0		566.0		562.3
Construction in progress
Property, Plant and Equipment
Gross property, plant and equipment	$ 32.0		$ 32.0		$ 21.9