Components of Total Equity and Comprehensive Income (Detail) - USD ($) $ in Thousands	3 Months Ended
	Aug. 31, 2017	Aug. 31, 2016
Stockholders Equity Note [Line Items]
Total equity, beginning of period	$ 1,438,700	$ 1,374,748
Net income	116,903	113,394
Other Comprehensive Income:
Foreign currency translation adjustments	44,478	(11,511)
Pension and other postretirement benefit liability adjustments, net of tax	629	5,704
Unrealized gain (loss) on securities, net of tax	(78)	1,604
Unrealized (loss) on derivatives, net of tax	(394)
Total other comprehensive income (loss)	44,635	(4,203)
Total Comprehensive Income	161,538	109,191
Dividends paid	(40,089)	(36,529)
Other noncontrolling interest activity	(65)	(912)
Shares repurchased and returned for taxes	(5,346)	(17,105)
Stock based compensation expense	7,465	8,171
Total Equity, end of period	1,562,203	1,437,564
Total RPM International Inc. Equity
Stockholders Equity Note [Line Items]
Total equity, beginning of period	1,436,061	1,372,335
Net income	116,416	112,769
Other Comprehensive Income:
Foreign currency translation adjustments	44,447	(11,511)
Pension and other postretirement benefit liability adjustments, net of tax	629	5,704
Unrealized gain (loss) on securities, net of tax	(78)	1,604
Unrealized (loss) on derivatives, net of tax	(394)
Total other comprehensive income (loss)	44,604	(4,203)
Total Comprehensive Income	161,020	108,566
Dividends paid	(40,089)	(36,529)
Shares repurchased and returned for taxes	(5,346)	(17,105)
Stock based compensation expense	7,465	8,171
Total Equity, end of period	1,559,111	1,435,438
Noncontrolling Interest
Stockholders Equity Note [Line Items]
Total equity, beginning of period	2,639	2,413
Net income	487	625
Other Comprehensive Income:
Foreign currency translation adjustments	31
Total other comprehensive income (loss)	31
Total Comprehensive Income	518	625
Other noncontrolling interest activity	(65)	(912)
Total Equity, end of period	$ 3,092	$ 2,126