Components of Total Equity and Comprehensive Income (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Nov. 30, 2018	Nov. 30, 2017	Nov. 30, 2018	Nov. 30, 2017
Stockholders Equity Note [Line Items]
Total equity, beginning of period	$ 1,613,379	$ 1,562,203	$ 1,633,538	$ 1,438,700
Net income	49,173	95,858	119,359	212,761
Other Comprehensive Income:
Foreign currency translation adjustments	(12,245)	(8,158)	(52,935)	36,320
Pension and other postretirement benefit liability adjustments, net of tax	3,428	3,066	6,483	3,695
Unrealized gain (loss) on securities and other, net of tax	(1,515)	2,549	962	2,471
Unrealized gain (loss) on derivatives, net of tax	2,349	(2,746)	3,271	(3,140)
Total other comprehensive (loss) income	(7,983)	(5,289)	(42,219)	39,346
Total Comprehensive Income	41,190	90,569	77,140	252,107
Dividends paid	(46,482)	(42,789)	(89,196)	(82,878)
Other	1,364		(1,467)
Other noncontrolling interest activity		(647)		(712)
Shares repurchased and returned for taxes	(2,879)	(6,779)	(16,466)	(12,125)
Share repurchases under repurchase program	(74,998)		(81,992)
Stock based compensation expense		6,964		14,429
Convertible bond redemption	(2,808)		(2,808)
Total Equity, end of period	1,536,046	1,609,521	1,536,046	1,609,521
SG&A
Other Comprehensive Income:
Stock based compensation expense	6,227		12,896
Restructuring Expense
Other Comprehensive Income:
Stock based compensation expense	1,053		4,401
Total RPM International Inc. Equity
Stockholders Equity Note [Line Items]
Total equity, beginning of period	1,610,447	1,559,111	1,630,773	1,436,061
Net income	49,224	95,463	118,988	211,879
Other Comprehensive Income:
Foreign currency translation adjustments	(12,336)	(8,086)	(52,768)	36,361
Pension and other postretirement benefit liability adjustments, net of tax	3,428	3,066	6,483	3,695
Unrealized gain (loss) on securities and other, net of tax	(1,515)	2,549	962	2,471
Unrealized gain (loss) on derivatives, net of tax	2,349	(2,746)	3,271	(3,140)
Total other comprehensive (loss) income	(8,074)	(5,217)	(42,052)	39,387
Total Comprehensive Income	41,150	90,246	76,936	251,266
Dividends paid	(46,482)	(42,789)	(89,196)	(82,878)
Other	797		(2,037)
Shares repurchased and returned for taxes	(2,879)	(6,779)	(16,466)	(12,125)
Share repurchases under repurchase program	(74,998)		(81,992)
Stock based compensation expense		6,964		14,429
Convertible bond redemption	(2,808)		(2,808)
Total Equity, end of period	1,532,507	1,606,753	1,532,507	1,606,753
Total RPM International Inc. Equity | SG&A
Other Comprehensive Income:
Stock based compensation expense	6,227		12,896
Total RPM International Inc. Equity | Restructuring Expense
Other Comprehensive Income:
Stock based compensation expense	1,053		4,401
Noncontrolling Interest
Stockholders Equity Note [Line Items]
Total equity, beginning of period	2,932	3,092	2,765	2,639
Net income	(51)	395	371	882
Other Comprehensive Income:
Foreign currency translation adjustments	91	(72)	(167)	(41)
Total other comprehensive (loss) income	91	(72)	(167)	(41)
Total Comprehensive Income	40	323	204	841
Other	567		570
Other noncontrolling interest activity		(647)		(712)
Total Equity, end of period	$ 3,539	$ 2,768	$ 3,539	$ 2,768