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Description of the Business and Summary of Significant Accounting Policies (Goodwill) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Aug. 03, 2020
Goodwill
Goodwill	$ 457,226	$ 452,915
Goodwill impairment loss	0	0	$ 0
Compensation expense for stock-based employee compensation plan	50,700	43,300	$ 38,700
Steel Operations
Goodwill
Goodwill	272,133	272,133
Metals Recycling Operations
Goodwill
Goodwill	183,168	178,857
Metals Recycling Operations \| OmniSource
Goodwill
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
Goodwill
Goodwill	1,925	$ 1,925
Zimmer, S.A. de C.V.
Goodwill
Goodwill				$ 7,700
Zimmer, S.A. de C.V. \| Metals Recycling Operations
Goodwill
Goodwill	$ 7,700