Revenue from Contracts with Customers - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Disaggregation of Revenue [Line Items]
Revenue	$ 834.1	$ 692.5
Percent of revenue	100.00%	100.00%
Nickel-based Alloys and Specialty Alloys [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	50.00%	43.00%
Precision and Engineered Strip [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	17.00%	20.00%
Precision Forgings, Casting and Components [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	15.00%	15.00%
Titanium and Titanium-based Alloys [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	10.00%	12.00%
Zirconium and Related Alloys [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	8.00%	10.00%
UNITED STATES
Disaggregation of Revenue [Line Items]
Revenue	$ 477.7	$ 399.9
Asia [Member]
Disaggregation of Revenue [Line Items]
Revenue	159.3	142.7
Europe [Member]
Disaggregation of Revenue [Line Items]
Revenue	159.9	113.1
CANADA
Disaggregation of Revenue [Line Items]
Revenue	19.0	17.3
South America, Middle East, and Other [Member]
Disaggregation of Revenue [Line Items]
Revenue	18.2	19.5
Aerospace and Defense Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	366.8	254.2
Jet Engines- Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue	196.6	106.1
Airframes- Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue	93.7	58.2
Defense [Member]
Disaggregation of Revenue [Line Items]
Revenue	76.5	89.9
Energy
Disaggregation of Revenue [Line Items]
Revenue	159.7	149.1
Oil & Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue	103.1	82.5
Specialty Energy [Member]
Disaggregation of Revenue [Line Items]
Revenue	56.6	66.6
Automotive Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	91.0	91.5
Electronic Devices Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	51.6	55.6
Construction Mining Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	52.0	42.5
Food Equipment and Appliances Market
Disaggregation of Revenue [Line Items]
Revenue	34.0	35.4
Medical Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	36.2	29.0
Other Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	42.8	35.2
Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	916.4	741.2
Operating Segments | High Performance Materials & Components
Disaggregation of Revenue [Line Items]
Revenue	$ 380.8	$ 265.2
Percent of revenue	100.00%	100.00%
Operating Segments | High Performance Materials & Components | Nickel-based Alloys and Specialty Alloys [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	48.00%	36.00%
Operating Segments | High Performance Materials & Components | Precision and Engineered Strip [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	0.00%	0.00%
Operating Segments | High Performance Materials & Components | Precision Forgings, Casting and Components [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	36.00%	43.00%
Operating Segments | High Performance Materials & Components | Titanium and Titanium-based Alloys [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	16.00%	21.00%
Operating Segments | High Performance Materials & Components | Zirconium and Related Alloys [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	0.00%	0.00%
Operating Segments | High Performance Materials & Components | UNITED STATES
Disaggregation of Revenue [Line Items]
Revenue	$ 156.4	$ 128.3
Operating Segments | High Performance Materials & Components | Asia [Member]
Disaggregation of Revenue [Line Items]
Revenue	44.2	20.1
Operating Segments | High Performance Materials & Components | Europe [Member]
Disaggregation of Revenue [Line Items]
Revenue	121.3	79.1
Operating Segments | High Performance Materials & Components | CANADA
Disaggregation of Revenue [Line Items]
Revenue	10.3	8.2
Operating Segments | High Performance Materials & Components | South America, Middle East, and Other [Member]
Disaggregation of Revenue [Line Items]
Revenue	9.4	5.2
Operating Segments | High Performance Materials & Components | Aerospace and Defense Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	257.6	179.8
Operating Segments | High Performance Materials & Components | Jet Engines- Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue	179.0	95.9
Operating Segments | High Performance Materials & Components | Airframes- Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue	37.2	26.5
Operating Segments | High Performance Materials & Components | Defense [Member]
Disaggregation of Revenue [Line Items]
Revenue	41.4	57.4
Operating Segments | High Performance Materials & Components | Energy
Disaggregation of Revenue [Line Items]
Revenue	47.2	30.5
Operating Segments | High Performance Materials & Components | Oil & Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue	17.1	8.3
Operating Segments | High Performance Materials & Components | Specialty Energy [Member]
Disaggregation of Revenue [Line Items]
Revenue	30.1	22.2
Operating Segments | High Performance Materials & Components | Automotive Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	2.9	2.0
Operating Segments | High Performance Materials & Components | Electronic Devices Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	0.5	0.3
Operating Segments | High Performance Materials & Components | Construction Mining Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	8.4	5.1
Operating Segments | High Performance Materials & Components | Food Equipment and Appliances Market
Disaggregation of Revenue [Line Items]
Revenue	0.0	0.0
Operating Segments | High Performance Materials & Components | Medical Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	13.2	11.2
Operating Segments | High Performance Materials & Components | Other Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	11.8	12.0
Operating Segments | Advanced Alloys & Solutions [Member]
Disaggregation of Revenue [Line Items]
Revenue	$ 535.6	$ 476.0
Percent of revenue	100.00%	100.00%
Operating Segments | Advanced Alloys & Solutions [Member] | Nickel-based Alloys and Specialty Alloys [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	52.00%	47.00%
Operating Segments | Advanced Alloys & Solutions [Member] | Precision and Engineered Strip [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	29.00%	31.00%
Operating Segments | Advanced Alloys & Solutions [Member] | Precision Forgings, Casting and Components [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	0.00%	0.00%
Operating Segments | Advanced Alloys & Solutions [Member] | Titanium and Titanium-based Alloys [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	5.00%	7.00%
Operating Segments | Advanced Alloys & Solutions [Member] | Zirconium and Related Alloys [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	14.00%	15.00%
Operating Segments | Advanced Alloys & Solutions [Member] | UNITED STATES
Disaggregation of Revenue [Line Items]
Revenue	$ 321.3	$ 271.6
Operating Segments | Advanced Alloys & Solutions [Member] | Asia [Member]
Disaggregation of Revenue [Line Items]
Revenue	115.1	122.6
Operating Segments | Advanced Alloys & Solutions [Member] | Europe [Member]
Disaggregation of Revenue [Line Items]
Revenue	38.6	34.0
Operating Segments | Advanced Alloys & Solutions [Member] | CANADA
Disaggregation of Revenue [Line Items]
Revenue	8.7	9.1
Operating Segments | Advanced Alloys & Solutions [Member] | South America, Middle East, and Other [Member]
Disaggregation of Revenue [Line Items]
Revenue	8.8	14.3
Operating Segments | Advanced Alloys & Solutions [Member] | Aerospace and Defense Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	109.2	74.4
Operating Segments | Advanced Alloys & Solutions [Member] | Jet Engines- Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue	17.6	10.2
Operating Segments | Advanced Alloys & Solutions [Member] | Airframes- Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue	56.5	31.7
Operating Segments | Advanced Alloys & Solutions [Member] | Defense [Member]
Disaggregation of Revenue [Line Items]
Revenue	35.1	32.5
Operating Segments | Advanced Alloys & Solutions [Member] | Energy
Disaggregation of Revenue [Line Items]
Revenue	112.5	118.6
Operating Segments | Advanced Alloys & Solutions [Member] | Oil & Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue	86.0	74.2
Operating Segments | Advanced Alloys & Solutions [Member] | Specialty Energy [Member]
Disaggregation of Revenue [Line Items]
Revenue	26.5	44.4
Operating Segments | Advanced Alloys & Solutions [Member] | Automotive Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	88.1	89.5
Operating Segments | Advanced Alloys & Solutions [Member] | Electronic Devices Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	51.1	55.3
Operating Segments | Advanced Alloys & Solutions [Member] | Construction Mining Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	43.6	37.4
Operating Segments | Advanced Alloys & Solutions [Member] | Food Equipment and Appliances Market
Disaggregation of Revenue [Line Items]
Revenue	34.0	35.4
Operating Segments | Advanced Alloys & Solutions [Member] | Medical Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	23.0	17.8
Operating Segments | Advanced Alloys & Solutions [Member] | Other Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	31.0	23.2
External Customers | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	834.1	692.5
External Customers | Operating Segments | High Performance Materials & Components
Disaggregation of Revenue [Line Items]
Revenue	341.6	240.9
External Customers | Operating Segments | Advanced Alloys & Solutions [Member]
Disaggregation of Revenue [Line Items]
Revenue	$ 492.5	$ 451.6