Revenue from Contracts with Customers - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Disaggregation of Revenue [Line Items]
Revenue	$ 1,038.1	$ 834.1
Percent of revenue	100.00%	100.00%
Nickel-based Alloys and Specialty Alloys [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	53.00%	50.00%
Precision and Engineered Strip [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	10.00%	17.00%
Precision Forgings, Casting and Components [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	16.00%	15.00%
Titanium and Titanium-based Alloys [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	14.00%	10.00%
Zirconium and Related Alloys [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	7.00%	8.00%
UNITED STATES
Disaggregation of Revenue [Line Items]
Revenue	$ 588.3	$ 477.7
Asia [Member]
Disaggregation of Revenue [Line Items]
Revenue	153.5	159.3
Europe [Member]
Disaggregation of Revenue [Line Items]
Revenue	238.6	159.9
CANADA
Disaggregation of Revenue [Line Items]
Revenue	23.2	19.0
South America, Middle East, and Other [Member]
Disaggregation of Revenue [Line Items]
Revenue	34.5	18.2
Aerospace and Defense Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	575.7	366.8
Jet Engines- Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue	310.9	196.6
Airframes- Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue	169.9	93.7
Defense [Member]
Disaggregation of Revenue [Line Items]
Revenue	94.9	76.5
Energy
Disaggregation of Revenue [Line Items]
Revenue	210.2	159.7
Oil & Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue	127.5	103.1
Specialty Energy [Member]
Disaggregation of Revenue [Line Items]
Revenue	82.7	56.6
Automotive Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	59.4	91.0
Electronic Devices Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	34.4	51.6
Construction Mining Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	40.4	52.0
Food Equipment and Appliances Market
Disaggregation of Revenue [Line Items]
Revenue	21.5	34.0
Medical Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	35.0	36.2
Other Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	61.5	42.8
Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	1,155.4	916.4
Operating Segments | High Performance Materials & Components
Disaggregation of Revenue [Line Items]
Revenue	$ 529.6	$ 380.8
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	45.00%	48.00%
Operating Segments | High Performance Materials & Components | Precision and Engineered Strip [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	1.00%	0.00%
Operating Segments | High Performance Materials & Components | Precision Forgings, Casting and Components [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	34.00%	36.00%
Operating Segments | High Performance Materials & Components | Titanium and Titanium-based Alloys [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	20.00%	16.00%
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	$ 196.5	$ 156.4
Operating Segments | High Performance Materials & Components | Asia [Member]
Disaggregation of Revenue [Line Items]
Revenue	44.0	44.2
Operating Segments | High Performance Materials & Components | Europe [Member]
Disaggregation of Revenue [Line Items]
Revenue	194.2	121.3
Operating Segments | High Performance Materials & Components | CANADA
Disaggregation of Revenue [Line Items]
Revenue	12.0	10.3
Operating Segments | High Performance Materials & Components | South America, Middle East, and Other [Member]
Disaggregation of Revenue [Line Items]
Revenue	24.4	9.4
Operating Segments | High Performance Materials & Components | Aerospace and Defense Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	395.4	257.6
Operating Segments | High Performance Materials & Components | Jet Engines- Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue	282.5	179.0
Operating Segments | High Performance Materials & Components | Airframes- Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue	71.0	37.2
Operating Segments | High Performance Materials & Components | Defense [Member]
Disaggregation of Revenue [Line Items]
Revenue	41.9	41.4
Operating Segments | High Performance Materials & Components | Energy
Disaggregation of Revenue [Line Items]
Revenue	27.3	47.2
Operating Segments | High Performance Materials & Components | Oil & Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue	2.4	17.1
Operating Segments | High Performance Materials & Components | Specialty Energy [Member]
Disaggregation of Revenue [Line Items]
Revenue	24.9	30.1
Operating Segments | High Performance Materials & Components | Automotive Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	6.3	2.9
Operating Segments | High Performance Materials & Components | Electronic Devices Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	0.5	0.5
Operating Segments | High Performance Materials & Components | Construction Mining Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	8.2	8.4
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	17.5	13.2
Operating Segments | High Performance Materials & Components | Other Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	15.9	11.8
Operating Segments | Advanced Alloys & Solutions
Disaggregation of Revenue [Line Items]
Revenue	$ 625.8	$ 535.6
Percent of revenue	100.00%	100.00%
Operating Segments | Advanced Alloys & Solutions | Nickel-based Alloys and Specialty Alloys [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	60.00%	52.00%
Operating Segments | Advanced Alloys & Solutions | Precision and Engineered Strip [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	19.00%	29.00%
Operating Segments | Advanced Alloys & Solutions | Precision Forgings, Casting and Components [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	0.00%	0.00%
Operating Segments | Advanced Alloys & Solutions | Titanium and Titanium-based Alloys [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	8.00%	5.00%
Operating Segments | Advanced Alloys & Solutions | Zirconium and Related Alloys [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	13.00%	14.00%
Operating Segments | Advanced Alloys & Solutions | UNITED STATES
Disaggregation of Revenue [Line Items]
Revenue	$ 391.8	$ 321.3
Operating Segments | Advanced Alloys & Solutions | Asia [Member]
Disaggregation of Revenue [Line Items]
Revenue	109.5	115.1
Operating Segments | Advanced Alloys & Solutions | Europe [Member]
Disaggregation of Revenue [Line Items]
Revenue	44.4	38.6
Operating Segments | Advanced Alloys & Solutions | CANADA
Disaggregation of Revenue [Line Items]
Revenue	11.2	8.7
Operating Segments | Advanced Alloys & Solutions | South America, Middle East, and Other [Member]
Disaggregation of Revenue [Line Items]
Revenue	10.1	8.8
Operating Segments | Advanced Alloys & Solutions | Aerospace and Defense Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	180.3	109.2
Operating Segments | Advanced Alloys & Solutions | Jet Engines- Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue	28.4	17.6
Operating Segments | Advanced Alloys & Solutions | Airframes- Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue	98.9	56.5
Operating Segments | Advanced Alloys & Solutions | Defense [Member]
Disaggregation of Revenue [Line Items]
Revenue	53.0	35.1
Operating Segments | Advanced Alloys & Solutions | Energy
Disaggregation of Revenue [Line Items]
Revenue	182.9	112.5
Operating Segments | Advanced Alloys & Solutions | Oil & Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue	125.1	86.0
Operating Segments | Advanced Alloys & Solutions | Specialty Energy [Member]
Disaggregation of Revenue [Line Items]
Revenue	57.8	26.5
Operating Segments | Advanced Alloys & Solutions | Automotive Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	53.1	88.1
Operating Segments | Advanced Alloys & Solutions | Electronic Devices Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	33.9	51.1
Operating Segments | Advanced Alloys & Solutions | Construction Mining Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	32.2	43.6
Operating Segments | Advanced Alloys & Solutions | Food Equipment and Appliances Market
Disaggregation of Revenue [Line Items]
Revenue	21.5	34.0
Operating Segments | Advanced Alloys & Solutions | Medical Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	17.5	23.0
Operating Segments | Advanced Alloys & Solutions | Other Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	45.6	31.0
External Customers | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	1,038.1	834.1
External Customers | Operating Segments | High Performance Materials & Components
Disaggregation of Revenue [Line Items]
Revenue	471.1	341.6
External Customers | Operating Segments | Advanced Alloys & Solutions
Disaggregation of Revenue [Line Items]
Revenue	$ 567.0	$ 492.5