Retirement Plans (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Compensation and Retirement Disclosure [Abstract]
Defined Contribution Plan, Cost Recognized	$ 92.5	$ 64.7	$ 21.0
Profit sharing component	$ 80.7	$ 59.3	$ 17.7
Percentage of employer's profit sharing contribution	8.00%	8.00%	8.00%
Employer's contribution to profit sharing plans for eligable employees	$ 64.5	$ 47.5	$ 14.1

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

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

- References

No definition available.

+ Details

Name:	us-gaap_CompensationAndRetirementDisclosureAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
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- 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=49170846&loc=d3e28014-114942

+ Details

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