Components of Total Equity and Comprehensive Income (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Feb. 28, 2018	Feb. 28, 2017	Feb. 28, 2018	Feb. 28, 2017
Stockholders Equity Note [Line Items]
Total equity, beginning of period	$ 1,609,521	$ 1,283,334	$ 1,438,700	$ 1,374,748
Net income	40,588	12,684	253,349	55,822
Other Comprehensive Income (Loss):
Foreign currency translation adjustments	31,133	16,576	67,453	(46,919)
Pension and other postretirement benefit liability adjustments, net of tax	2,279	3,222	5,974	12,516
Unrealized (loss) on securities, net of tax	(2,380)	2,577	91	3,286
Unrealized (loss) on derivatives, net of tax	(2,137)		(5,277)
Total other comprehensive income (loss)	28,895	22,375	68,241	(31,117)
Total Comprehensive Income	69,483	35,059	321,590	24,705
Dividends paid	(42,794)	(40,076)	(125,672)	(116,680)
Other noncontrolling interest activity	(517)	(153)	(1,229)	(1,959)
Shares repurchased and returned for taxes	(2,940)	(429)	(15,065)	(20,092)
Stock based compensation expense	3,269	7,992	17,698	25,005
Total Equity, end of period	1,636,022	1,285,727	1,636,022	1,285,727
Total RPM International Inc. Equity
Stockholders Equity Note [Line Items]
Total equity, beginning of period	1,606,753	1,281,432	1,436,061	1,372,335
Net income	40,227	11,928	252,106	53,771
Other Comprehensive Income (Loss):
Foreign currency translation adjustments	31,101	16,576	67,462	(46,919)
Pension and other postretirement benefit liability adjustments, net of tax	2,279	3,222	5,974	12,516
Unrealized (loss) on securities, net of tax	(2,380)	2,577	91	3,286
Unrealized (loss) on derivatives, net of tax	(2,137)		(5,277)
Total other comprehensive income (loss)	28,863	22,375	68,250	(31,117)
Total Comprehensive Income	69,090	34,303	320,356	22,654
Dividends paid	(42,794)	(40,076)	(125,672)	(116,680)
Shares repurchased and returned for taxes	(2,940)	(429)	(15,065)	(20,092)
Stock based compensation expense	3,269	7,992	17,698	25,005
Total Equity, end of period	1,633,378	1,283,222	1,633,378	1,283,222
Noncontrolling Interest
Stockholders Equity Note [Line Items]
Total equity, beginning of period	2,768	1,902	2,639	2,413
Net income	361	756	1,243	2,051
Other Comprehensive Income (Loss):
Foreign currency translation adjustments	32		(9)
Total other comprehensive income (loss)	32		(9)
Total Comprehensive Income	393	756	1,234	2,051
Other noncontrolling interest activity	(517)	(153)	(1,229)	(1,959)
Total Equity, end of period	$ 2,644	$ 2,505	$ 2,644	$ 2,505