Segment and Geographic Information - Sales by Product Group (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Revenue, Major Customer [Line Items]
Sales	$ 294.5	$ 290.8	$ 270.8	$ 270.8	$ 248.4	$ 242.7	$ 233.5	$ 245.5	$ 1,126.9	$ 970.1	$ 1,009.3
Process Materials
Revenue, Major Customer [Line Items]
Sales									401.8	387.4	387.3
Advanced Materials
Revenue, Major Customer [Line Items]
Sales									427.9	369.3	356.1
Equipment and Installations
Revenue, Major Customer [Line Items]
Sales									235.4	150.8	208.3
Site Services
Revenue, Major Customer [Line Items]
Sales									58.2	62.6	57.6
Corp segment
Revenue, Major Customer [Line Items]
Sales									$ 3.6	$ 0.0	$ 0.0