Description of the Business and Significant Accounting Policies (Goodwill) (Details) - USD ($)	3 Months Ended
Mar. 31, 2021	Dec. 31, 2020
Goodwill
Goodwill	$ 456,378,000	$ 457,226,000
Steel Operations
Goodwill
Goodwill	272,133,000	272,133,000
Metals Recycling Operations
Goodwill
Goodwill	182,320,000	183,168,000
Metals Recycling Operations \| OmniSource
Goodwill
Goodwill decrease due to tax benefit related to the normal amortization of the component	848,000
Steel Fabrication Operations
Goodwill
Goodwill	$ 1,925,000	$ 1,925,000

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/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(10)(1))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=120320667&loc=SL49117168-202975

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=99380562&loc=d3e13770-109266

Name:	us-gaap_Goodwill
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant