The number of locations under collective bargaining arrangements.

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The percentage of employees covered by a collective bargaining agreement as of the balance sheet date.

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Percentage of net revenue of the entity's external sales accounted for by the reportable unit.

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The number of locations under collective bargaining arrangements that expire within the next twelve months.

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Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

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Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer.

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Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Percentage of subsidiary's or equity method investee's stock owned by parent immediately after all stock transactions.

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Description of the Business and Significant Accounting Policies (Description of the Business) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 segment item	Dec. 31, 2017	Dec. 31, 2016 USD ($)
Segment Reporting Information
Workforce represented by collective bargaining agreements (as a percent)	9.00%
Number of Locations Subject to Collective Bargaining Agreements \| item	6
Number of locations subject to collective bargaining agreements that expire \| item	0
Impairment charges			$ 132,839
Segment Reporting Information
Number of reporting segments \| segment	3
Steel Operations
Segment Reporting Information
Percentage of external net sales	75.00%	72.00%	72.00%
Metals Recycling Operations
Segment Reporting Information
Percentage of external net sales	13.00%	15.00%	15.00%
Steel Fabrication Operations
Segment Reporting Information
Percentage of external net sales	8.00%	9.00%	9.00%
Mining Resources
Segment Reporting Information
Subsidiary or Equity Method Investee, Cumulative Percentage Ownership after All Transactions	84.00%		82.00%
Business Combination, Consideration Transferred			$ 15,100
Minnesota ironmaking operations
Segment Reporting Information
Impairment charges			127,300
Minnesota ironmaking operations \| Noncontrolling Interests
Segment Reporting Information
Impairment charges			13,100
Parent Company [Member]
Segment Reporting Information
Impairment charges			12,700
Parent Company [Member] \| Minnesota ironmaking operations
Segment Reporting Information
Impairment charges			72,900
Guarantors
Segment Reporting Information
Impairment charges			5,500
Combined Non-Guarantors
Segment Reporting Information
Impairment charges			$ 116,445