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Acquisitions (Details) $ in Millions | 2 Months Ended | 3 Months Ended | 5 Months Ended | 10 Months Ended | 12 Months Ended |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Dec. 31, 2018 USD ($) location | Dec. 31, 2018 USD ($) location | Sep. 30, 2018 USD ($) | Jun. 30, 2018 USD ($) | Mar. 31, 2018 USD ($) | Dec. 31, 2017 USD ($) | Sep. 30, 2017 USD ($) | Jun. 30, 2017 USD ($) | Mar. 31, 2017 USD ($) | Dec. 31, 2018 USD ($) location | Dec. 31, 2018 USD ($) location | Dec. 31, 2018 USD ($) location | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) | Nov. 01, 2018 location | Oct. 23, 2018 | Oct. 22, 2018 | Jan. 01, 2016 location | Dec. 31, 2015 USD ($)
Acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net sales |  | $ 2,814.0 | $ 2,974.5 | $ 2,988.9 | $ 2,757.1 | $ 2,376.4 | $ 2,450.1 | $ 2,475.2 | $ 2,419.3 |  |  | $ 11,534.5 | $ 9,721.0 | $ 8,613.4 |  |  |  |  |
Allocation of the total purchase price of the acquisitions to the fair value of the assets acquired and liabilities assumed |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Goodwill value | $ 1,870.8 | 1,870.8 |  |  |  | 1,842.6 |  |  |  | $ 1,870.8 | $ 1,870.8 | 1,870.8 | 1,842.6 | 1,827.4 |  |  |  |  | $ 1,724.8
Summary purchase price allocation information for all acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Tax deductible goodwill amount | 685.4 | 685.4 |  |  |  |  |  |  |  | 685.4 | 685.4 | 685.4 |  |  |  |  |  |  |
Summary Information for Equity Method Transaction |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Consideration paid for additional ownership percentage |  |  |  |  |  |  |  |  |  |  |  | 29.0 |  |  |  |  |  |  |
Trade names |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Allocation of the total purchase price of the acquisitions to the fair value of the assets acquired and liabilities assumed |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Intangible assets not subject to amortization | 18.3 | 18.3 |  |  |  | 3.7 |  |  |  | 18.3 | 18.3 | 18.3 | 3.7 | 38.2 |  |  |  |  |
Summary purchase price allocation information for all acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Intangible assets not subject to amortization | 18.3 | $ 18.3 |  |  |  | $ 3.7 |  |  |  | $ 18.3 | $ 18.3 | 18.3 | 3.7 | 38.2 |  |  |  |  |
Customer relationships |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary purchase price allocation information for all acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Intangible assets acquired subject to amortization |  |  |  |  |  |  |  |  |  |  |  | $ 24.8 | $ 3.7 | $ 76.8 |  |  |  |  |
Weighted average lives of identifiable intangible assets |  |  |  |  |  |  |  |  |  |  |  | 10 years | 10 years | 15 years 6 months |  |  |  |  |
All Metals |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net sales | $ 4.2 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Locations acquiree provides logistics services from | location |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 6 |  |  |  |
Acero Prime S. de R.L. de C.V. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  |  |  |  | $ 41.0 |  |  |  |  |  |  |
Ownership interest acquired (as a percent) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 40.00% |  |  |
Ownership interest prior to acquisition (as a percent) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 60.00% |  |
Total ownership percentage (as a percent) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 100.00% |  |  |
Number of locations of the acquiree entity | location | 4 | 4 |  |  |  |  |  |  |  | 4 | 4 | 4 |  |  |  |  |  |  |
Summary Information for Equity Method Transaction |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Consideration paid for additional ownership percentage |  |  |  |  |  |  |  |  |  |  |  | $ 29.0 |  |  |  |  |  |  |
Decrease in noncontrolling interest |  |  |  |  |  |  |  |  |  |  |  | 19.7 |  |  |  |  |  |  |
Decrease in Reliance Stockholder's equity |  |  |  |  |  |  |  |  |  |  |  | 9.3 |  |  |  |  |  |  |
KMS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  |  | $ 11.9 |  |  |  |  |  |  |  |  |
DuBose |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  |  |  | $ 26.9 |  |  |  |  |  |  |  |
All Metals, DuBose and KMS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Allocation of the total purchase price of the acquisitions to the fair value of the assets acquired and liabilities assumed |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cash | $ 2.4 | $ 2.4 |  |  |  |  |  |  |  | 2.4 | 2.4 | 2.4 |  |  |  |  |  |  |
Accounts receivable | 13.1 | 13.1 |  |  |  |  |  |  |  | 13.1 | 13.1 | 13.1 |  |  |  |  |  |  |
Inventories | 10.0 | 10.0 |  |  |  |  |  |  |  | 10.0 | 10.0 | 10.0 |  |  |  |  |  |  |
Property, plant and equipment | 20.2 | 20.2 |  |  |  |  |  |  |  | 20.2 | 20.2 | 20.2 |  |  |  |  |  |  |
Goodwill value | 33.8 | 33.8 |  |  |  |  |  |  |  | 33.8 | 33.8 | 33.8 |  |  |  |  |  |  |
Intangible assets subject to amortization | 25.0 | 25.0 |  |  |  |  |  |  |  | 25.0 | 25.0 | 25.0 |  |  |  |  |  |  |
Intangible assets not subject to amortization | 18.3 | 18.3 |  |  |  |  |  |  |  | 18.3 | 18.3 | 18.3 |  |  |  |  |  |  |
Other current and long-term assets | 1.1 | 1.1 |  |  |  |  |  |  |  | 1.1 | 1.1 | 1.1 |  |  |  |  |  |  |
Total assets acquired | 123.9 | 123.9 |  |  |  |  |  |  |  | 123.9 | 123.9 | 123.9 |  |  |  |  |  |  |
Current and long-term debt | 25.9 | 25.9 |  |  |  |  |  |  |  | 25.9 | 25.9 | 25.9 |  |  |  |  |  |  |
Deferred taxes | 7.8 | 7.8 |  |  |  |  |  |  |  | 7.8 | 7.8 | 7.8 |  |  |  |  |  |  |
Other current and long-term liabilities | 9.2 | 9.2 |  |  |  |  |  |  |  | 9.2 | 9.2 | 9.2 |  |  |  |  |  |  |
Total liabilities assumed | 42.9 | 42.9 |  |  |  |  |  |  |  | 42.9 | 42.9 | 42.9 |  |  |  |  |  |  |
Net assets acquired | 81.0 | 81.0 |  |  |  |  |  |  |  | 81.0 | 81.0 | 81.0 |  |  |  |  |  |  |
Summary purchase price allocation information for all acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Intangible assets not subject to amortization | 18.3 | 18.3 |  |  |  |  |  |  |  | 18.3 | 18.3 | 18.3 |  |  |  |  |  |  |
Ferguson |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Sales since acquisition date |  |  |  |  |  |  |  |  |  |  |  | 39.4 |  |  |  |  |  |  |
Alaska Steel |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  |  |  |  | 26.7 |  |  |  |  |  |  |
Best Manufacturing |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  |  |  |  | 26.3 |  |  |  |  |  |  |
Tubular Steel |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  |  |  |  | 174.4 |  |  |  |  |  |  |
Number of locations of the acquiree entity | location |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 6 |
2018 Acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary purchase price allocation information for all acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Tax deductible goodwill amount | 21.3 | 21.3 |  |  |  |  |  |  |  | 21.3 | 21.3 | 21.3 |  |  |  |  |  |  |
2016 Acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Allocation of the total purchase price of the acquisitions to the fair value of the assets acquired and liabilities assumed |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cash |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1.5 |  |  |  |  |
Accounts receivable |  |  |  |  |  |  |  |  |  |  |  |  |  | 14.1 |  |  |  |  |
Inventories |  |  |  |  |  |  |  |  |  |  |  |  |  | 66.6 |  |  |  |  |
Property, plant and equipment |  |  |  |  |  |  |  |  |  |  |  |  |  | 62.2 |  |  |  |  |
Goodwill value |  |  |  |  |  |  |  |  |  |  |  |  |  | 104.7 |  |  |  |  |
Intangible assets subject to amortization |  |  |  |  |  |  |  |  |  |  |  |  |  | 77.1 |  |  |  |  |
Intangible assets not subject to amortization |  |  |  |  |  |  |  |  |  |  |  |  |  | 38.2 |  |  |  |  |
Other current and long-term assets |  |  |  |  |  |  |  |  |  |  |  |  |  | 0.5 |  |  |  |  |
Total assets acquired |  |  |  |  |  |  |  |  |  |  |  |  |  | 364.9 |  |  |  |  |
Current and long-term debt |  |  |  |  |  |  |  |  |  |  |  |  |  | 6.1 |  |  |  |  |
Other current and long-term liabilities |  |  |  |  |  |  |  |  |  |  |  |  |  | 7.3 |  |  |  |  |
Total liabilities assumed |  |  |  |  |  |  |  |  |  |  |  |  |  | 13.4 |  |  |  |  |
Net assets acquired |  |  |  |  |  |  |  |  |  |  |  |  |  | 351.5 |  |  |  |  |
Summary purchase price allocation information for all acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Intangible assets not subject to amortization |  |  |  |  |  |  |  |  |  |  |  |  |  | 38.2 |  |  |  |  |
Tax deductible goodwill amount |  |  |  |  |  |  |  |  |  |  |  |  |  | 104.7 |  |  |  |  |
2018, 2017 and 2016 Acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary purchase price allocation information for all acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Tax deductible goodwill amount | $ 21.3 | $ 21.3 |  |  |  |  |  |  |  | $ 21.3 | $ 21.3 | $ 21.3 |  | $ 104.7 |  |  |  |  |

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- Definition Amount of current and long-term debt assumed at the acquisition date. + References No definition available. + Details
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- Definition The amount of other current and noncurrent assets recognized as of the acquisition date. + References No definition available. + Details
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- Definition Represents the reduction in Reliance equity from purchase of non-controlling interest for consideration in excess of reduction in non-controlling interest. + References No definition available. + Details
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- Definition Weighted average amortization period of finite-lived intangible assets acquired either individually or as part of a group of assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16265-109275 + Details
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- Definition Percentage of voting equity interests acquired at the acquisition date in the business combination. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=79982066&loc=d3e1392-128463 + Details
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- Definition This element represents the amount of revenue of the acquiree since the acquisition date included in the consolidated income statement for the reporting period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1) -URI http://asc.fasb.org/extlink&oid=79982066&loc=d3e1392-128463 + Details
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- Definition Amount of assets acquired at the acquisition date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=84161108&loc=d3e4845-128472 + Details
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- Definition Amount of currency on hand as well as demand deposits with banks or financial institutions, acquired at the acquisition date. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=84161108&loc=d3e4845-128472 + Details
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- Definition Amount due from customers or clients for goods or services, including trade receivables, that have been delivered or sold in the normal course of business, and amounts due from others, including related parties expected to be converted to cash, sold or exchanged within one year or the normal operating cycle, if longer, acquired at the acquisition date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=84161108&loc=d3e4845-128472 + Details
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- Definition Amount of deferred tax liability attributable to taxable temporary difference assumed at the acquisition date that are classified as noncurrent. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=84161108&loc=d3e4845-128472 + Details
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- Definition Amount of assets, excluding financial assets and goodwill, that lack physical substance, having a projected indefinite period of benefit, acquired at the acquisition date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=84161108&loc=d3e4845-128472 + Details
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- Definition The amount of identifiable intangible assets recognized as of the acquisition date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 55 -Paragraph 37 -URI http://asc.fasb.org/extlink&oid=84160947&loc=d3e2207-128464 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=84161108&loc=d3e4845-128472 + Details
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- Definition The amount of inventory recognized as of the acquisition date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=84161108&loc=d3e4845-128472 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 55 -Paragraph 37 -URI http://asc.fasb.org/extlink&oid=84160947&loc=d3e2207-128464 + Details
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