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Description of the Business and Significant Accounting Policies (Goodwill) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Goodwill
Goodwill	$ 429,645	$ 386,893
Goodwill, Impairment Loss	0	0	$ 0
Compensation expense for stock options	38,700	36,600	30,400
Steel Operations \| Columbus Flat Roll Division
Goodwill
Goodwill	19,682	19,682
Steel Operations \| The Techs
Goodwill
Goodwill	142,783	142,783
Steel Operations \| Heartland Flat Roll Division
Goodwill
Goodwill	46,143
Steel Operations \| Vulcan Threaded Products Inc
Goodwill
Goodwill	7,824	7,824
Steel Operations \| Roanoke Bar Division
Goodwill
Goodwill	29,041	29,041
Metals Recycling Operations \| OmniSource
Goodwill
Goodwill	182,247	185,638
Goodwill, Impairment Loss			$ 5,500
Goodwill decrease due to tax benefit related to the normal amortization of the component	3,400
Goodwill, Impaired, Accumulated Impairment Loss	346,800	346,800
Steel Fabrication Operations \| New Millennium Building Systems
Goodwill
Goodwill	1,925	1,925
Guarantors
Goodwill
Goodwill	$ 429,645	379,069
Combined Non-Guarantors
Goodwill
Goodwill		$ 7,824