Segment Information, Geographic and Product Data - Schedule of Results of Operation, Depreciation and Amortization, Capital Expenditures and Total Assets by Reportable Segments (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Consolidated net sales	$ 641.4	$ 609.9	$ 556.5	$ 572.4	$ 618.0	$ 572.2	$ 487.8	$ 479.8	$ 2,380.2	$ 2,157.7	$ 1,797.6
Consolidated operating income	67.9	$ 73.2	$ 55.4	$ 45.0	60.0	$ 45.7	$ 41.4	$ 42.2	241.4	189.3	121.5
Consolidated depreciation and amortization									121.5	116.6	117.8
Consolidated capital expenditures									180.3	135.0	98.5
Consolidated total assets	3,187.8				3,007.0				3,187.8	3,007.0
Corporate costs (including loss on divestiture of business)
Segment Reporting Information [Line Items]
Consolidated operating income									(72.7)	(66.4)	(60.8)
Consolidated depreciation and amortization									4.9	3.9	4.0
Consolidated capital expenditures									37.1	41.6	29.7
Consolidated total assets	192.5				193.2				192.5	193.2
Intersegment
Segment Reporting Information [Line Items]
Consolidated net sales									(66.9)	(75.8)	(30.6)
Consolidated operating income									1.9	(2.8)	1.5
Consolidated depreciation and amortization									(0.8)	(0.8)	(0.8)
Consolidated capital expenditures									(1.2)	(1.8)	(0.4)
Consolidated total assets	(18.7)				(11.9)				(18.7)	(11.9)
Specialty Alloys Operations | Operating
Segment Reporting Information [Line Items]
Consolidated net sales									1,967.3	1,803.8	1,461.6
Consolidated operating income									282.2	232.4	172.3
Consolidated depreciation and amortization									95.2	93.3	94.0
Consolidated capital expenditures									92.7	63.6	52.2
Consolidated total assets	2,349.2				2,312.1				2,349.2	2,312.1
Performance Engineered Products | Operating
Segment Reporting Information [Line Items]
Consolidated net sales									479.8	429.7	366.6
Consolidated operating income									30.0	26.1	8.5
Consolidated depreciation and amortization									22.2	20.2	20.6
Consolidated capital expenditures									51.7	31.6	$ 17.0
Consolidated total assets	$ 664.8				$ 513.6				$ 664.8	$ 513.6