Retirement Plans (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Retirement Plans
Total expenses recognized under 401 (k) Plan	$ 39.4	$ 25.2	$ 22.9
Percentage of employer's profit sharing contribution	8.00%	8.00%	2.00%
Profit sharing component	36.3stld_ProfitSharingComponent	23.1stld_ProfitSharingComponent	20.5stld_ProfitSharingComponent
Employer's contribution to profit sharing plans for eligible employees	$ 29.0	$ 18.5	$ 14.3

Represents the employer's contribution as percentage of consolidated pretax earnings, to the profit sharing plans.

No definition available.

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

- Definition

The aggregate amount of the employer's profit sharing component of which a portion was contributed to a defined benefit plan and a portion was paid directly to the participants of the profit sharing plan.

+ References

No definition available.

+ Details

Name:	stld_ProfitSharingComponent
Namespace Prefix:	stld_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The amount of the profit sharing component of the contribution made by the employer to the defined benefit plan.

+ References

No definition available.

+ Details

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Namespace Prefix:	stld_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

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

- Definition

The amount of the cost recognized during the period for defined contribution plans.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 70

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6414718&loc=d3e28014-114942

+ Details

Name:	us-gaap_DefinedContributionPlanCostRecognized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration