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Description of the Business and Significant Accounting Policies (Goodwill) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill
Goodwill	$ 386,893	$ 393,351
Compensation expense for stock options	36,600	30,400	$ 27,100
Steel Operations \| Columbus Flat Roll Division
Goodwill
Goodwill	19,682	19,682
Steel Operations \| The Techs
Goodwill
Goodwill	142,783	142,783
Steel Operations \| Vulcan Steel Products [Member]
Goodwill
Goodwill	7,824	7,824
Steel Operations \| Roanoke Bar Division
Goodwill
Goodwill	29,041	29,041
Metals Recycling Operations \| Butler Flat Roll Division, Structural and Rail Division, and Engineered Bar Division
Goodwill
Goodwill	95,000	95,000
Metals Recycling Operations \| OmniSource
Goodwill
Goodwill	90,638	97,096
Goodwill, Impairment Loss	5,500	341,300
Goodwill decrease due to tax benefit related to the normal amortization of the component	6,500
Goodwill, Impaired, Accumulated Impairment Loss	346,800
Indefinite-lived intangible assets impairment charge		68,500
Steel Fabrication Operations \| New Millennium Building Systems
Goodwill
Goodwill	$ 1,925	$ 1,925