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Segment Information - Summary of sale by product and service (Details) - item	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Information
Number of reportable segments	1	1	1
Sales (as a percent)	100.00%	100.00%	100.00%
Carbon steel
Segment Information
Sales (as a percent)	52.00%	52.00%	52.00%
Aluminum
Segment Information
Sales (as a percent)	19.00%	20.00%	19.00%
Stainless steel
Segment Information
Sales (as a percent)	14.00%	14.00%	14.00%
Alloy
Segment Information
Sales (as a percent)	6.00%	5.00%	7.00%
Toll processing and logistics
Segment Information
Sales (as a percent)	4.00%	4.00%	3.00%
Other
Segment Information
Sales (as a percent)	5.00%	5.00%	5.00%

X

- Definition

Represents the percentage of revenue from sale of goods and services.

+ References

No definition available.

+ Details

Name:	rs_SalesRevenueGoodsAndServicesNetPercentage
Namespace Prefix:	rs_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- 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

X

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

X

- Details

Name:	us-gaap_ProductOrServiceAxis=rs_CarbonSteelMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ProductOrServiceAxis=rs_AluminumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ProductOrServiceAxis=rs_StainlessSteelMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ProductOrServiceAxis=rs_AlloySteelMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ProductOrServiceAxis=rs_TollProcessingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ProductOrServiceAxis=rs_OtherProductsOrServicesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: