Description of the Business and Significant Accounting Policies (Description of the Business) (Details) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2024 USD ($) segment item	Dec. 31, 2023 USD ($)
Segment Reporting Information
Number of reportable segments \| segment	4
Redeemable noncontrolling interests	$ 171,212	$ 171,212
United Steel Supply, LLC
Segment Reporting Information
Noncontrolling interest, ownership percentage	90.00%	90.00%
Redeemable noncontrolling interests	$ 60,000	$ 60,000
Mesabi Nugget
Segment Reporting Information
Noncontrolling interest, ownership percentage	86.00%	86.00%
Redeemable noncontrolling interests	$ 111,200	$ 111,200
Unity Aluminum, Inc \| Aluminum Operations
Segment Reporting Information
Number Of Satellite Recycled Aluminum Slab Centers \| item	2
Noncontrolling interest, ownership percentage	94.40%

The number of satellite recycled aluminum slab centers in aluminum operations.

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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-18

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As of the reporting date, the aggregate carrying amount of all noncontrolling interests which are redeemable by the (parent) entity (1) at a fixed or determinable price on a fixed or determinable date, (2) at the option of the holder of the noncontrolling interest, or (3) upon occurrence of an event that is not solely within the control of the (parent) entity. This item includes noncontrolling interest holder's ownership (or holders' ownership) regardless of the type of equity interest (common, preferred, other) including all potential organizational (legal) forms of the investee entity.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 480
-SubTopic 10
-Subparagraph (12)(c)
-Section S99
-Paragraph 3A
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480244/480-10-S99-3A

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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-Topic 480
-SubTopic 10
-Subparagraph 14
-Paragraph 3A
-Section S99
-Publisher FASB
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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-Topic 480
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-Subparagraph 15
-Paragraph 3A
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-Publisher FASB
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Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 480
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-Subparagraph (16)(c)
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-Section S99
-Publisher FASB
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- Definition

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

+ References

No definition available.

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