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Pension Plans - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
 12 Months Ended 5 Months Ended
May 31, 2014
May 31, 2015
Pension Benefits, U.S. Plans    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Contribution to retirement plans in current fiscal year $ 53.1us-gaap_DefinedBenefitPlansEstimatedFutureEmployerContributionsInCurrentFiscalYear
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_UnitedStatesPensionPlansOfUSEntityDefinedBenefitMember		  
Pension Benefits, Non-U.S. Plans    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Contribution to retirement plans in current fiscal year 6.3us-gaap_DefinedBenefitPlansEstimatedFutureEmployerContributionsInCurrentFiscalYear
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_ForeignPensionPlansDefinedBenefitMember		  
DayGlo Pension Plans | Scenario, Forecast    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Contribution to retirement plans in current fiscal year   $ 0.2us-gaap_DefinedBenefitPlansEstimatedFutureEmployerContributionsInCurrentFiscalYear
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= rpm_DaygloPensionPlansMember
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioForecastMember