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, 2019	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Jun. 30, 2019
Net Sales:
Consolidated net sales	$ 573.0	$ 556.5	$ 1,158.4	$ 1,128.9
Operating Income (Loss):
Consolidated operating income	55.0	55.4	114.8	100.4
Depreciation and Amortization:
Consolidated depreciation and amortization	30.5	30.3	61.0	60.1
Capital Expenditures:
Consolidated capital expenditures	46.7	40.1	94.3	81.7
Total Assets:
Consolidated total assets	3,403.6		3,403.6		$ 3,187.8
Corporate
Operating Income (Loss):
Consolidated operating income	(21.9)	(18.4)	(41.0)	(34.2)
Depreciation and Amortization:
Consolidated depreciation and amortization	1.3	1.2	2.6	2.4
Capital Expenditures:
Consolidated capital expenditures	16.4	6.5	32.6	14.2
Total Assets:
Consolidated total assets	233.0		233.0		192.5
Intersegment
Net Sales:
Consolidated net sales	(16.0)	(18.0)	(31.1)	(32.8)
Operating Income (Loss):
Consolidated operating income	0.2	0.4	0.2	1.2
Depreciation and Amortization:
Consolidated depreciation and amortization	(0.2)	(0.2)	(0.5)	(0.3)
Capital Expenditures:
Consolidated capital expenditures	0.0	(0.5)	0.0	(0.8)
Total Assets:
Consolidated total assets	(4.3)		(4.3)		(18.7)
Specialty Alloys Operations | Operating
Net Sales:
Consolidated net sales	483.0	461.6	974.1	937.1
Operating Income (Loss):
Consolidated operating income	76.3	69.0	157.3	121.7
Depreciation and Amortization:
Consolidated depreciation and amortization	23.2	23.8	46.8	47.5
Capital Expenditures:
Consolidated capital expenditures	24.9	20.8	50.1	41.4
Total Assets:
Consolidated total assets	2,479.2		2,479.2		2,349.2
Performance Engineered Products | Operating
Net Sales:
Consolidated net sales	106.0	112.9	215.4	224.6
Operating Income (Loss):
Consolidated operating income	0.4	4.4	(1.7)	11.7
Depreciation and Amortization:
Consolidated depreciation and amortization	6.2	5.5	12.1	10.5
Capital Expenditures:
Consolidated capital expenditures	5.4	$ 13.3	11.6	$ 26.9
Total Assets:
Consolidated total assets	$ 695.7		$ 695.7		$ 664.8