Description of the Business and Significant Accounting Policies - Goodwill (Details) - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2016	Dec. 31, 2015
Goodwill
Goodwill	$ 394,275	$ 397,470
OmniSource
Goodwill
Goodwill decrease due to tax benefit related to the normal amortization of the component	3,200
Metals Recycling Operations \| OmniSource
Goodwill
Goodwill	105,844	109,039
Metals Recycling Operations \| Butler Flat Roll Division, Structural and Rail Division, and Engineered Bar Division
Goodwill
Goodwill	95,000	95,000
Steel Operations \| The Techs
Goodwill
Goodwill	142,783	142,783
Steel Operations \| Roanoke Bar Division
Goodwill
Goodwill	29,041	29,041
Steel Operations \| Columbus Flat Roll Division
Goodwill
Goodwill	19,682	19,682
Steel Fabrication Operations \| New Millennium Building Systems
Goodwill
Goodwill	$ 1,925	$ 1,925

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266

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