Business Segments - Schedule of results of operation, depreciation and amortization, capital expenditures and total assets by reportable segments (Details) - USD ($) $ in Millions	3 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Jun. 30, 2020
Net Sales:
Consolidated net sales	$ 353.3	$ 585.4
Operating (Loss) Income:
Consolidated operating (loss) income	(48.8)	59.8
Depreciation and Amortization:
Consolidated depreciation and amortization	30.9	30.6
Capital Expenditures:
Consolidated capital expenditures	33.3	47.5
Total Assets:
Consolidated total assets	3,128.7		$ 3,227.2
Corporate
Operating (Loss) Income:
Consolidated operating (loss) income	(26.6)	(19.1)
Depreciation and Amortization:
Consolidated depreciation and amortization	1.7	1.3
Capital Expenditures:
Consolidated capital expenditures	9.4	16.2
Total Assets:
Consolidated total assets	471.3		428.9
Intersegment
Net Sales:
Consolidated net sales	(9.2)	(15.1)
Operating (Loss) Income:
Consolidated operating (loss) income	0.0	(0.1)
Depreciation and Amortization:
Consolidated depreciation and amortization	0.0	(0.2)
Capital Expenditures:
Consolidated capital expenditures	(0.1)	(0.1)
Total Assets:
Consolidated total assets	(15.9)		(9.2)
Specialty Alloys Operations | Operating
Net Sales:
Consolidated net sales	300.7	491.1
Operating (Loss) Income:
Consolidated operating (loss) income	(18.6)	81.0
Depreciation and Amortization:
Consolidated depreciation and amortization	23.2	23.6
Capital Expenditures:
Consolidated capital expenditures	21.8	25.2
Total Assets:
Consolidated total assets	2,170.7		2,259.0
Performance Engineered Products | Operating
Net Sales:
Consolidated net sales	61.8	109.4
Operating (Loss) Income:
Consolidated operating (loss) income	(3.6)	(2.0)
Depreciation and Amortization:
Consolidated depreciation and amortization	6.0	5.9
Capital Expenditures:
Consolidated capital expenditures	2.2	$ 6.2
Total Assets:
Consolidated total assets	$ 502.6		$ 548.5