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Business Segments - Major Customers (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenue, Major Customer [Line Items]
Major customer, percentage revenue, net									10.00%
Net sales	$ 389.1	$ 392.9	$ 401.9	$ 421.2	$ 435.5	$ 438.0	$ 473.1	$ 490.0
Glencore [Member]
Revenue, Major Customer [Line Items]
Net sales									$ 1,025.5	$ 1,191.6	$ 1,204.5
Southwire [Member]
Revenue, Major Customer [Line Items]
Net sales									$ 195.9	$ 235.4	$ 222.4

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For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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