Description of the Business and Significant Accounting Policies (Goodwill) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Goodwill
Goodwill	$ 386,045	$ 386,893
OmniSource
Goodwill
Goodwill decrease due to tax benefit related to the normal amortization of the component	848
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 | OmniSource
Goodwill
Goodwill	89,790	90,638
Metals Recycling Operations | Indiana Steel Mills [Member]
Goodwill
Goodwill	95,000	95,000
Steel Fabrication Operations | New Millennium Building Systems
Goodwill
Goodwill	$ 1,925	$ 1,925