Goodwill and Other Intangible Assets, net - Schedule of Goodwill (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2020	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Changes in the carrying amount of goodwill by reportable segment
Goodwill gross, beginning balance			$ 372.2
Accumulated impairment losses, beginning balance			(81.8)
Total goodwill net, beginning balance			290.4
Impairment	$ 0.0	$ 0.0	(52.8)	$ 0.0
Other			3.8
Goodwill gross, ending balance			376.0
Accumulated impairment losses, ending balance			(134.6)
Total goodwill net, ending balance			241.4
Specialty Alloy Operations
Changes in the carrying amount of goodwill by reportable segment
Total goodwill net, beginning balance			195.5
Total goodwill net, ending balance			195.5
Performance Engineered Products
Changes in the carrying amount of goodwill by reportable segment
Total goodwill net, beginning balance			94.9
Impairment			(52.8)
Other			3.8
Accumulated impairment losses, ending balance			(134.6)
Total goodwill net, ending balance			$ 45.9