Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	May 31, 2021	May 31, 2020	May 31, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net Income	$ 503,500	$ 305,082	$ 267,687
Other Comprehensive Income, Before Tax:
Foreign Currency Translation Adjustments	148,492	(71,839)	(73,594)
Pension and Other Postretirement Benefit Liability Adjustments
Net Gain (Loss) Arising During the Period	88,958	(109,358)	(87,525)
Prior Service Cost Arising During the Period		893	22
Less: Amortization of Prior Service (Credit) Included in Net Periodic Pension Cost	(309)	(246)	(132)
Less: Amortization of Net Loss and Settlement Recognition	33,344	21,176	14,848
Effect of Exchange Rates on Amounts Included for Pensions	(8,009)	1,188	2,002
Pension and Other Postretirement Benefit Liability Adjustments	113,984	(86,347)	(70,785)
Unrealized Gain (Loss) on Available-For-Sale Securities
Unrealized Holding Gains (Losses) During the Period	(593)	1,210	458
Less: Reclassification Adjustments for Losses (Gains) Included in Net Income	(268)		1,626
Unrealized Gain (Loss) on Available-For-Sale Securities	(861)	1,210	2,084
Unrealized Gain (Loss) on Derivatives	(31,087)	(6,315)	4,713
Other Comprehensive Income (Loss), Before Tax	230,528	(163,291)	(137,582)
Income Tax Expense (Benefit) Related to Components of Other Comprehensive Income	(27,783)	23,403	19,068
Other Comprehensive Income (Loss), After Tax	202,745	(139,888)	(118,514)
Comprehensive Income	706,245	165,194	149,173
Less: Comprehensive Income Attributable to Noncontrolling Interests	988	678	1,195
Comprehensive Income Attributable to RPM International Inc. Stockholders	$ 705,257	$ 164,516	$ 147,978