Segment and Geographic Information - Segments (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting Information [Line Items]
Revenues	$ 350.8	$ 350.0	$ 340.7	$ 330.8	$ 294.5	$ 290.8	$ 270.8	$ 270.8	$ 1,372.3	$ 1,126.9	$ 970.1
Operating Income (Loss)	99.3	96.2	89.4	89.1	70.9	81.0	69.9	78.8	374.0	300.6	276.2
Business separation, restructuring and cost reduction actions	(3.9)	$ (6.7)	$ (8.2)	$ (1.8)	(10.2)	$ (6.0)	$ (6.1)	$ (3.2)	(20.6)	(25.5)	(0.9)
Depreciation and Amortization									50.8	46.0	46.9
Equity Affiliates’ Income									0.0	0.0	0.2
Total Assets	1,505.3				1,255.6				1,505.3	1,255.6	1,052.1
Expenditures for Long-Lived Assets									115.4	64.0	35.8
Operating Segments
Segment Reporting Information [Line Items]
Operating Income (Loss)									394.6	326.1	277.1
Operating Segments | Materials
Segment Reporting Information [Line Items]
Revenues									885.6	829.7	756.7
Operating Income (Loss)									286.5	274.9	249.6
Depreciation and Amortization									47.7	43.1	44.4
Total Assets	862.5				782.6				862.5	782.6	741.7
Expenditures for Long-Lived Assets									93.1	45.7	34.4
Operating Segments | Delivery Systems and Services
Segment Reporting Information [Line Items]
Revenues									483.7	293.6	213.4
Operating Income (Loss)									135.5	71.7	50.8
Depreciation and Amortization									2.1	1.4	2.1
Total Assets	144.9				110.9				144.9	110.9	104.0
Expenditures for Long-Lived Assets									1.0	1.7	0.7
Operating Segments | Corporate
Segment Reporting Information [Line Items]
Revenues									3.0	3.6	0.0
Operating Income (Loss)									(27.4)	(20.5)	(23.3)
Depreciation and Amortization									1.0	1.5	0.4
Total Assets	$ 497.9				$ 362.1				497.9	362.1	206.4
Expenditures for Long-Lived Assets									21.3	16.6	0.7
Segment Reconciling Items
Segment Reporting Information [Line Items]
Business separation, restructuring and cost reduction actions									$ (20.6)	$ (25.5)	$ (0.9)