Components of Total Equity and Comprehensive Income (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Nov. 30, 2017	Nov. 30, 2016	Nov. 30, 2017	Nov. 30, 2016
Stockholders Equity Note [Line Items]
Total equity, beginning of period	$ 1,562,203	$ 1,437,564	$ 1,438,700	$ 1,374,748
Net Income (Loss)	95,858	(70,256)	212,761	43,138
Other Comprehensive Income (Loss):
Foreign currency translation adjustments	(8,158)	(51,984)	36,320	(63,495)
Pension and other postretirement benefit liability adjustments, net of tax	3,066	3,590	3,695	9,294
Unrealized gain (loss) on securities, net of tax	2,549	(895)	2,471	709
Unrealized (loss) on derivatives, net of tax	(2,746)		(3,140)
Total other comprehensive income (loss)	(5,289)	(49,289)	39,346	(53,492)
Total Comprehensive Income (Loss)	90,569	(119,545)	252,107	(10,354)
Dividends paid	(42,789)	(40,075)	(82,878)	(76,604)
Other noncontrolling interest activity	(647)	(894)	(712)	(1,806)
Shares repurchased and returned for taxes	(6,779)	(2,558)	(12,125)	(19,663)
Stock based compensation expense	6,964	8,842	14,429	17,013
Total Equity, end of period	1,609,521	1,283,334	1,609,521	1,283,334
Total RPM International Inc. Equity
Stockholders Equity Note [Line Items]
Total equity, beginning of period	1,559,111	1,435,438	1,436,061	1,372,335
Net Income (Loss)	95,463	(70,926)	211,879	41,843
Other Comprehensive Income (Loss):
Foreign currency translation adjustments	(8,086)	(51,984)	36,361	(63,495)
Pension and other postretirement benefit liability adjustments, net of tax	3,066	3,590	3,695	9,294
Unrealized gain (loss) on securities, net of tax	2,549	(895)	2,471	709
Unrealized (loss) on derivatives, net of tax	(2,746)		(3,140)
Total other comprehensive income (loss)	(5,217)	(49,289)	39,387	(53,492)
Total Comprehensive Income (Loss)	90,246	(120,215)	251,266	(11,649)
Dividends paid	(42,789)	(40,075)	(82,878)	(76,604)
Shares repurchased and returned for taxes	(6,779)	(2,558)	(12,125)	(19,663)
Stock based compensation expense	6,964	8,842	14,429	17,013
Total Equity, end of period	1,606,753	1,281,432	1,606,753	1,281,432
Noncontrolling Interest
Stockholders Equity Note [Line Items]
Total equity, beginning of period	3,092	2,126	2,639	2,413
Net Income (Loss)	395	670	882	1,295
Other Comprehensive Income (Loss):
Foreign currency translation adjustments	(72)		(41)
Total other comprehensive income (loss)	(72)		(41)
Total Comprehensive Income (Loss)	323	670	841	1,295
Other noncontrolling interest activity	(647)	(894)	(712)	(1,806)
Total Equity, end of period	$ 2,768	$ 1,902	$ 2,768	$ 1,902