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Leases - Additional Information (Detail) - USD ($) $ in Millions | 12 Months Ended
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May. 31, 2015 | May. 31, 2014 | May. 31, 2013
Lease and Rental Expense [Line Items] |  |  |
Rental expenses for all operating lease | $ 53.8 | $ 50.9 | $ 46.5

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- Definition Lease and Rental Expense [Line Items] + References No definition available. + Details
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Namespace Prefix: | rpm_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Amount of lease operating expense related to property used in oil and gas production. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6453985&loc=d3e41499-112717 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 10 -Paragraph a -Subparagraph 17 -Article 4 + Details
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