Represents the annual anticipated production capacity of facility.

No definition available.

Name:	stld_AnnualProductionCapacityOfFacilityAnticipated
Namespace Prefix:	stld_
Data Type:	num:massItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the actual annual production of facility.

+ References

No definition available.

+ Details

Name:	stld_AnnualProductionOfFacilityActual
Namespace Prefix:	stld_
Data Type:	num:massItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of agreements under collective bargaining arrangements that are to expire within the next twelve months.

+ References

No definition available.

+ Details

Name:	stld_CollectiveBargainingArrangementsAgreementsNumber
Namespace Prefix:	stld_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents number of galvanizing lines to be used in galvanizing of specific types of flat rolled steels in non-automotive applications.

+ References

No definition available.

+ Details

Name:	stld_NumberOfGalvanizingLines
Namespace Prefix:	stld_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the number of iron making initiatives.

+ References

No definition available.

+ Details

Name:	stld_NumberOfIronMakingInitiatives
Namespace Prefix:	stld_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the number of plants.

+ References

No definition available.

+ Details

Name:	stld_NumberOfPlants
Namespace Prefix:	stld_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of years subsequent to achievement of certain performance measures.

+ References

No definition available.

+ Details

Name:	stld_NumberOfYearsSubsequentToAchievementOfPerformanceMeasures
Namespace Prefix:	stld_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of ownership interest in facility.

+ References

No definition available.

+ Details

Name:	stld_PercentageOfOwnershipInterestInFacility
Namespace Prefix:	stld_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The percentage of employees covered by a collective bargaining agreement as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	stld_PercentageOfWorkforceSubjectToCollectiveBargainingArrangements
Namespace Prefix:	stld_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The period of planned outage used to complete the groundwork necessary for the implementation of further improvements.

+ References

No definition available.

+ Details

Name:	stld_PeriodOfPlannedOutage
Namespace Prefix:	stld_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of net revenue of the entity's external sales accounted for by the reportable unit.

+ References

No definition available.

+ Details

Name:	stld_SegmentRevenuesFromExternalCustomersNetPercentage
Namespace Prefix:	stld_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of employees covered by a collective bargaining agreement that expires within the next twelve months.

+ References

No definition available.

+ Details

Name:	stld_WorkforceSubjectToCollectiveBargainingArrangements
Namespace Prefix:	stld_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of locations under collective bargaining arrangements that expire within the next twelve months.

+ References

No definition available.

+ Details

Name:	stld_WorkforceSubjectToCollectiveBargainingArrangementsLocationsNumber
Namespace Prefix:	stld_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_AccountingPoliciesAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

+ References

No definition available.

+ Details

Name:	us-gaap_NumberOfReportableSegments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

As of the reporting date, the aggregate carrying amount of all noncontrolling interests which are redeemable by the (parent) entity (1) at a fixed or determinable price on a fixed or determinable date, (2) at the option of the holder of the noncontrolling interest, or (3) upon occurrence of an event that is not solely within the control of the (parent) entity. This item includes noncontrolling interest holder's ownership (or holders' ownership) regardless of the type of equity interest (common, preferred, other) including all potential organizational (legal) forms of the investee entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 480

-SubTopic 10

-Section S99

-Paragraph 3A

-Subparagraph 14

-URI http://asc.fasb.org/extlink&oid=14643745&loc=SL6540498-122764

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Emerging Issues Task Force (EITF)

-Number D-98

-Paragraph 43

-Subparagraph b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 480

-SubTopic 10

-Section S99

-Paragraph 3A

-Subparagraph (12)(c)

-URI http://asc.fasb.org/extlink&oid=14643745&loc=SL6540498-122764

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Emerging Issues Task Force (EITF)

-Number D-98

-Paragraph 43

-Subparagraph c

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 480

-SubTopic 10

-Section S99

-Paragraph 3A

-Subparagraph (16)(c)

-URI http://asc.fasb.org/extlink&oid=14643745&loc=SL6540498-122764

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 480

-SubTopic 10

-Section S99

-Paragraph 3A

-Subparagraph 15

-URI http://asc.fasb.org/extlink&oid=14643745&loc=SL6540498-122764

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Accounting Research Bulletin (ARB)

-Number 51

-Paragraph 27

-Subparagraph c

-Appendix A

+ Details

Name:	us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_SegmentReportingInformationLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Description of the Business and Summary of Significant Accounting Policies (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2012 t	Dec. 31, 2011 t	Dec. 31, 2010 t
Description of the Business and Summary of Significant Accounting Policies
Number of reporting segments		3
Workforce represented by collective bargaining agreements (as a percent)		10.00%
Number of collective bargaining agreements that expires in 2013		1
Number of employees under a collective bargaining agreement that expires in 2013		115
Number of locations subject to collective bargaining agreements that expire in 2013		1
Segment Reporting Information
Redeemable noncontrolling interests	98,814	98,814	70,694
Mesabi Nugget
Segment Reporting Information
Number of years subsequent to achievement of performance measures		3 years
Steel Operations
Segment Reporting Information
Percentage of external net sales		62.00%	61.00%	61.00%
Flat Roll Division
Segment Reporting Information
Percentage of external net sales		27.00%	27.00%	28.00%
Number of galvanizing lines		3
Metals Recycling and Ferrous Resources Operations
Segment Reporting Information
Number of iron making initiatives		2
Percentage of external net sales		32.00%	35.00%	35.00%
Redeemable noncontrolling interests	84,300	84,300	65,700
Metals Recycling and Ferrous Resources Operations \| Mesabi Nugget
Segment Reporting Information
Percentage of ownership interest in facility		81.00%
Period of planned outage in the fall of 2012 used to complete the groundwork necessary for the implementation of further improvements expected to be made	42 days
Designed annual production capacity of facility (in metric tons)		500,000
Actual annual production (in metric tons)		169,000	156,000	75,000
Metals Recycling and Ferrous Resources Operations \| Mining Resources
Segment Reporting Information
Percentage of ownership interest in facility		80.00%
Actual annual production (in metric tons)		56,000
Redeemable noncontrolling interests	14,500	14,500	5,000
Steel Fabrication Operations
Segment Reporting Information
Percentage of external net sales		5.00%	3.00%	3.00%
Number of plants		6