Debt Instrument, Number of Tranches

No definition available.

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

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=120520924&loc=SL6031897-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

+ Details

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

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Definition

Percentage price of original principal amount of debt at which debt can be redeemed by the issuer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph e
-URI http://asc.fasb.org/extlink&oid=75038535&loc=d3e64711-112823

+ Details

Name:	us-gaap_DebtInstrumentRedemptionPricePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of principal amount of debt redeemed.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentRedemptionPricePercentageOfPrincipalAmountRedeemed
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=120520924&loc=SL6031897-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

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

Long-Term Debt - Senior Unsecured Notes (Details) $ in Thousands	1 Months Ended			12 Months Ended
	Oct. 31, 2020	Jun. 30, 2020	Dec. 31, 2019 USD ($)	Dec. 31, 2020 USD ($) loan
Long Term Debt
Long-term Debt, Gross			$ 2,764,472	$ 3,158,658
Outstanding Balance			2,734,344	$ 3,102,676
Senior Notes
Long Term Debt
Debt Instrument, Number of Tranches \| loan				7
5 1/4% Senior Notes due 2023
Long Term Debt
Long-term Debt, Gross			$ 400,000
Stated interest rate			5.25%
Redemption price of debt instrument (as a percent)		100.875%
2.800% senior notes due 2024
Long Term Debt
Long-term Debt, Gross			$ 400,000	$ 400,000
Stated interest rate				2.80%
Redemption price of debt instrument (as a percent)				100.00%
2.400% senior notes due 2025
Long Term Debt
Long-term Debt, Gross				$ 400,000
Stated interest rate				2.40%
Redemption price of debt instrument (as a percent)				100.00%
5.000% senior notes due 2026
Long Term Debt
Long-term Debt, Gross			400,000	$ 400,000
Stated interest rate				5.00%
5.000% senior notes due 2026 \| Maximum
Long Term Debt
Maximum redemption of debt instrument (as a percent)				35.00%
5.000% senior notes due 2026 \| Debt Instrument, Redemption, Period One [Member]
Long Term Debt
Redemption price of debt instrument (as a percent)				105.00%
5.000% senior notes due 2026 \| Debt Instrument, Redemption, Period Two [Member]
Long Term Debt
Redemption price of debt instrument (as a percent)				102.50%
5.000% senior notes due 2026 \| Debt Instrument, Redemption, Period Three [Member]
Long Term Debt
Redemption price of debt instrument (as a percent)				101.667%
5.000% senior notes due 2026 \| Debt Instrument, Redemption, Period Four [Member]
Long Term Debt
Redemption price of debt instrument (as a percent)				100.833%
5.000% senior notes due 2026 \| Debt Instrument, Redemption, Period Five [Member]
Long Term Debt
Redemption price of debt instrument (as a percent)				100.00%
1.650% senior notes due 2027
Long Term Debt
Long-term Debt, Gross				$ 350,000
Stated interest rate				1.65%
Redemption price of debt instrument (as a percent)				100.00%
3.450% senior notes due 2030
Long Term Debt
Long-term Debt, Gross			600,000	$ 600,000
Stated interest rate				3.45%
Redemption price of debt instrument (as a percent)				100.00%
3.250% senior notes due 2031
Long Term Debt
Long-term Debt, Gross				$ 500,000
Stated interest rate				3.25%
Redemption price of debt instrument (as a percent)				100.00%
3.250% senior notes due 2050
Long Term Debt
Long-term Debt, Gross				$ 400,000
Stated interest rate				3.25%
Redemption price of debt instrument (as a percent)				100.00%
5.500% senior notes due 2024
Long Term Debt
Long-term Debt, Gross			$ 500,000
Stated interest rate		5.50%	5.50%
Redemption price of debt instrument (as a percent)		102.75%
4.125% senior notes due 2025
Long Term Debt
Long-term Debt, Gross			$ 350,000
Stated interest rate	4.125%		4.125%
Redemption price of debt instrument (as a percent)	102.063%
5.125% senior notes due 2021
Long Term Debt
Stated interest rate				5.125%
Redemption price of debt instrument (as a percent)			100.00%
US Treasury (UST) Interest Rate [Member] \| 2.800% senior notes due 2024
Long Term Debt
Debt Instrument, Basis Spread on Variable Rate				0.20%
US Treasury (UST) Interest Rate [Member] \| 2.400% senior notes due 2025
Long Term Debt
Debt Instrument, Basis Spread on Variable Rate				0.35%
US Treasury (UST) Interest Rate [Member] \| 5.000% senior notes due 2026
Long Term Debt
Debt Instrument, Basis Spread on Variable Rate				0.50%
US Treasury (UST) Interest Rate [Member] \| 1.650% senior notes due 2027
Long Term Debt
Debt Instrument, Basis Spread on Variable Rate				0.20%
US Treasury (UST) Interest Rate [Member] \| 3.450% senior notes due 2030
Long Term Debt
Debt Instrument, Basis Spread on Variable Rate				0.25%
US Treasury (UST) Interest Rate [Member] \| 3.250% senior notes due 2031
Long Term Debt
Debt Instrument, Basis Spread on Variable Rate				0.40%
US Treasury (UST) Interest Rate [Member] \| 3.250% senior notes due 2050
Long Term Debt
Debt Instrument, Basis Spread on Variable Rate				0.30%