Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	May 31, 2020	May 31, 2019	May 31, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net Income	$ 305,082	$ 267,687	$ 339,257
Other Comprehensive Income, Before Tax:
Foreign Currency Translation Adjustments	(71,839)	(73,594)	10,857
Pension and Other Postretirement Benefit Liabilities
Net (Loss) Arising During the Period	(109,358)	(87,525)	(3,489)
Prior Service Cost Arising During the Period	893	22	61
Less: Amortization of Prior Service Cost Included in Net Periodic Pension Cost	(246)	(132)	(121)
Less: Amortization of Net Loss and Settlement Recognition	21,176	14,848	16,738
Effect of Exchange Rates on Amounts Included for Pensions	1,188	2,002	(1,814)
Pension and Other Postretirement Benefit Liability Adjustments	(86,347)	(70,785)	11,375
Unrealized Gains on Available-For-Sale Securities
Unrealized Holding Gains (Losses) During the Period	1,210	458	(1,459)
Less: Reclassification Adjustments for Losses (Gains) Included in Net Income		1,626	(1,835)
Unrealized Gain (Loss) on Securities	1,210	2,084	(3,294)
Unrealized Gain (Loss) on Derivatives	(6,315)	4,713	(359)
Other Comprehensive (Loss) Income, Before Tax	(163,291)	(137,582)	18,579
Income Tax Expense (Benefit) Related to Components of Other Comprehensive Income	23,403	19,068	(3,773)
Other Comprehensive (Loss) Income, After Tax	(139,888)	(118,514)	14,806
Comprehensive Income	165,194	149,173	354,063
Less: Comprehensive Income Attributable to Noncontrolling Interests	678	1,195	1,354
Comprehensive Income Attributable to RPM International Inc. Stockholders	$ 164,516	$ 147,978	$ 352,709