Business, Product and Geographical Area Information and Concentration of Risk - Schedule of Significant Segment Expenses Provided To CODM (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Segment Reporting Information [Line Items]
Net sales	$ 3,024.0	$ 3,087.0	$ 3,427.9
Cost of products sold, excluding depreciation and amortization	2,691.1	2,754.9	3,180.2
Hedged cost of alloyed metal	1,567.8	1,621.1	2,045.2
Manufacturing costs	805.2	809.9	773.0
Plant overhead	170.5	164.6	162.3
Freight costs	91.6	103.3	125.5
Other cost of products sold	56.0	56.0	74.2
Depreciation and amortization	116.4	108.6	106.9
Selling, general, administrative, research and development	120.8	122.7	110.9
Research and development costs	2.2	2.9	1.9
Employee costs	83.3	80.0	69.9
Other selling, general and administrative costs	35.3	39.8	39.1
Goodwill impairment	0.0	0.0	20.5
Restructuring costs	7.6	5.0	2.2
Other operating charges, net	0.4	0.0	3.2
Interest expense	43.7	46.9	48.3
Other income, net - Note 13	(19.5)	(7.4)	(6.4)
Income tax provision (benefit)	16.7	9.1	(8.3)
Net income (loss)	$ 46.8	$ 47.2	$ (29.6)