Represents the share liability to the plan to be settled in cash.

No definition available.

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Period Type:	instant

- Definition

Represents the number of shares of the entity to be contributed to the plan as a result of acquisition.

+ References

No definition available.

+ Details

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- Definition

Period expense (income) related to postemployment benefits.

+ References

No definition available.

+ Details

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

- References

No definition available.

+ Details

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Data Type:	xbrli:stringItemType
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Period Type:	duration

- Definition

Amount of benefit for defined benefit plan expected to be paid in five fiscal years after fifth fiscal year following current fiscal year.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of benefit for defined benefit plan expected to be paid in next fiscal year following current fiscal year.

+ References

+ Details

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

- Definition

Amount of benefit for defined benefit plan expected to be paid in fifth fiscal year following current fiscal year.

+ References

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of benefit for defined benefit plan expected to be paid in fourth fiscal year following current fiscal year.

+ References

+ Details

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

- Definition

Amount of benefit for defined benefit plan expected to be paid in third fiscal year following current fiscal year.

+ References

+ Details

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

- Definition

Amount of benefit for defined benefit plan expected to be paid in second fiscal year following current fiscal year.

+ References

+ Details

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

- Definition

For a classified balance sheet, the carrying amount as of the balance sheet date of the portion of the obligations recognized for the various benefits provided to former or inactive employees, their beneficiaries, and covered dependents after employment but before retirement that is payable after one year (or beyond the operating cycle if longer).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 712
-SubTopic 10
-Section 25
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6410138&loc=d3e79708-111665

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 712
-SubTopic 10
-Section 25
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=6410138&loc=d3e79691-111665

+ Details

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

- References

No definition available.

+ Details

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

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RetirementPlanTypeAxis=us-gaap_PensionPlansDefinedBenefitMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RetirementPlanTypeAxis=rs_SupplementalBonusPlanMember
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Employee Benefits - Postretirement Plan and Summary Information for All Defined Benefit Plans (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Apr. 30, 2006	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
SERPs
Summary of benefit payments under the Company's various defined benefit plans, which reflect expected future employee service, as appropriate, expected to be paid in the future periods
2021		$ 0.9
2022		12.0
2023		0.9
2024		0.8
2025		0.8
2026-2030		3.6
Defined Benefit Plans
Summary of benefit payments under the Company's various defined benefit plans, which reflect expected future employee service, as appropriate, expected to be paid in the future periods
2021		2.0
2022		2.3
2023		2.5
2024		2.7
2025		2.9
2026-2030		$ 16.7
Supplemental Bonus Plan
Stock-Based Compensation
Number of shares of the entity to be contributed to the plan as a result of acquisition	258,006
Share liability to the plan to be settled in cash		53,197
Cash equivalent of share liability to the plan		$ 6.3
Expense (income) from mark to market adjustment		$ (0.2)	$ 3.3	$ (0.8)