Segment Information - Segments (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Sep. 30, 2018
Segment Reporting Information [Line Items]
Revenues	$ 324.3	$ 350.0	$ 990.0	$ 1,021.5
Business separation, restructuring and cost reduction actions	(141.4)	(6.7)	(156.3)	(16.7)
Operating Income (Loss)	(47.5)	96.3	130.9	275.2
Total Assets	1,458.7		1,458.7		$ 1,505.3
Operating Segments
Segment Reporting Information [Line Items]
Operating Income (Loss)	93.9	103.0	287.2	291.9
Operating Segments | Materials
Segment Reporting Information [Line Items]
Revenues	214.3	218.5	652.5	652.0
Operating Income (Loss)	67.6	71.5	200.6	209.3
Total Assets	910.2		910.2		862.5
Operating Segments | Delivery Systems and Services
Segment Reporting Information [Line Items]
Revenues	109.4	130.7	335.7	367.1
Operating Income (Loss)	31.5	37.2	101.1	103.6
Total Assets	167.0		167.0		144.9
Operating Segments | Corporate
Segment Reporting Information [Line Items]
Revenues	0.6	0.8	1.8	2.4
Operating Income (Loss)	(5.2)	(5.7)	(14.5)	(21.0)
Total Assets	381.5		381.5		$ 497.9
Segment Reconciling Items
Segment Reporting Information [Line Items]
Business separation, restructuring and cost reduction actions	$ (141.4)	$ (6.7)	$ (156.3)	$ (16.7)