Summary of Significant Accounting Policies, Narrative (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Significant accounting policies
Inventory Write-down	$ 0.0	$ 4.9
Workers Compensation Liability Undiscounted	$ 26.8		$ 26.8
Workers' Compensation Discount, Percent	2.00%		2.00%
Accrued liabilities for employee healthcare benefits	$ 3.8		$ 3.6
Fabricated Products
Significant accounting policies
(Shortfalls) excess of current cost over the stated LIFO value of inventory	$ (1.9)		$ 8.5

Significant accounting policies [Line Items]

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- Definition

Workers Compensation Liability, Undiscounted

+ References

No definition available.

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Carrying value as of the balance sheet date of obligations, excluding pension and other postretirement benefits, incurred through that date and payable for perquisites provided to employees pertaining to services received from them.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.15(a))
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- Definition

Amount by which inventory stated at last-in first-out (LIFO) is less than (in excess of) inventory stated at other inventory cost methods.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section S99
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-Subparagraph (SX 210.5-02.6(c))
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Amount of loss from reductions in inventory due to subsequent measurement adjustments, including, but not limited to, physical deterioration, obsolescence, or changes in price levels.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition

Percent discount applied to worker's compensation reserve liability to reduce the reserve to present value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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