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Business Segments - Major Customers (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended		9 Months Ended		12 Months Ended
	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue, Major Customer [Line Items]
Major customer, percentage revenue, net									10.00%
Net sales	$ 435.5	$ 490.0	$ 486.9	$ 454.5	$ 473.1	$ 470.0	$ 438.0	$ 481.8
Glencore [Member]
Revenue, Major Customer [Line Items]
Net sales									$ 1,191.6	$ 1,204.5	$ 1,198.1
Southwire [Member]
Revenue, Major Customer [Line Items]
Net sales									$ 235.4	$ 222.4	$ 77.2

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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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