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, 2018	Sep. 30, 2017	Jun. 30, 2018
Net Sales:
Consolidated net sales	$ 572.4	$ 479.8
Operating Income:
Consolidated operating income	45.0	42.2
Depreciation and Amortization:
Consolidated depreciation and amortization	29.7	28.7
Capital Expenditures:
Consolidated capital expenditures	41.6	28.9
Total Assets:
Consolidated total assets	3,007.7		$ 3,007.0
Corporate
Operating Income:
Consolidated operating income	(15.8)	(12.9)
Depreciation and Amortization:
Consolidated depreciation and amortization	1.2	0.9
Capital Expenditures:
Consolidated capital expenditures	7.7	7.1
Total Assets:
Consolidated total assets	158.5		193.2
Intersegment
Net Sales:
Consolidated net sales	(14.8)	(17.7)
Operating Income:
Consolidated operating income	0.7	(0.7)
Depreciation and Amortization:
Consolidated depreciation and amortization	(0.2)	(0.3)
Capital Expenditures:
Consolidated capital expenditures	(0.3)	(0.3)
Total Assets:
Consolidated total assets	(10.2)		(11.9)
Specialty Alloys Operations | Operating
Net Sales:
Consolidated net sales	475.5	396.8
Operating Income:
Consolidated operating income	52.8	50.5
Depreciation and Amortization:
Consolidated depreciation and amortization	23.7	23.1
Capital Expenditures:
Consolidated capital expenditures	20.6	17.2
Total Assets:
Consolidated total assets	2,319.0		2,312.1
Performance Engineered Products | Operating
Net Sales:
Consolidated net sales	111.7	100.7
Operating Income:
Consolidated operating income	7.3	5.3
Depreciation and Amortization:
Consolidated depreciation and amortization	5.0	5.0
Capital Expenditures:
Consolidated capital expenditures	13.6	$ 4.9
Total Assets:
Consolidated total assets	$ 540.4		$ 513.6