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Goodwill Impairment - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Mar. 31, 2020	Dec. 31, 2019
Goodwill [Line Items]
Goodwill	$ 238.4		$ 238.4			$ 525.8
Decrease of goodwill during period			(287.4)
Impairment of goodwill	0.0	$ 0.0	287.0	$ 0.0
Goodwill, foreign currency translation loss			(0.4)
Accumulated goodwill impairment loss	528.0		528.0			$ 241.0
Forged Products
Goodwill [Line Items]
Goodwill	173.4		173.4		$ 460.4
Reporting unit, percentage of fair value in excess of carrying amount						30.00%
Specialty Materials
Goodwill [Line Items]
Goodwill	$ 65.0		$ 65.0