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		6 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2017
Net Sales:
Net Sales:	$ 487.8	$ 427.4	$ 967.5	$ 816.3
Operating Income:
Operating Income:	40.8	15.4	82.5	16.8
Depreciation and Amortization:
Depreciation and Amortization:	29.2	29.9	58.0	58.7
Capital Expenditures:
Capital Expenditures:	26.8	18.5	55.7	45.1
Total Assets:
Total Assets:	2,944.1		2,944.1		$ 2,878.1
Corporate
Operating Income:
Operating Income:	(13.9)	(16.0)	(26.9)	(29.8)
Depreciation and Amortization:
Depreciation and Amortization:	0.9	0.9	1.8	1.7
Capital Expenditures:
Capital Expenditures:	9.6	7.7	16.7	15.2
Total Assets:
Total Assets:	148.4		148.4		167.2
Segment Reconciling Items
Operating Income:
Pension earnings, interest and deferrals	(0.5)	(5.6)	(1.1)	(12.7)
Intersegment
Net Sales:
Net Sales:	(23.3)	(4.4)	(41.1)	(9.1)
Operating Income:
Operating Income:	(2.1)	0.6	(2.6)	0.7
Depreciation and Amortization:
Depreciation and Amortization:	(0.2)	0.1	(0.4)	(0.5)
Capital Expenditures:
Capital Expenditures:	(0.3)	0.0	(0.5)	(0.1)
Total Assets:
Total Assets:	(17.9)		(17.9)		(15.5)
Specialty Alloys Operations | Operating
Net Sales:
Net Sales:	406.3	348.6	803.1	663.7
Operating Income:
Operating Income:	49.8	35.6	100.3	60.6
Depreciation and Amortization:
Depreciation and Amortization:	23.4	23.7	46.5	47.2
Capital Expenditures:
Capital Expenditures:	11.2	8.3	28.4	23.0
Total Assets:
Total Assets:	2,337.9		2,337.9		2,292.1
Performance Engineered Products | Operating
Net Sales:
Net Sales:	104.8	83.2	205.5	161.7
Operating Income:
Operating Income:	7.5	0.8	12.8	(2.0)
Depreciation and Amortization:
Depreciation and Amortization:	5.1	5.2	10.1	10.3
Capital Expenditures:
Capital Expenditures:	6.3	$ 2.5	11.1	$ 7.0
Total Assets:
Total Assets:	$ 475.7		$ 475.7		$ 434.3