Components of Total Equity and Comprehensive Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Nov. 30, 2014	Nov. 30, 2013	Nov. 30, 2014	Nov. 30, 2013
Stockholders Equity Note [Line Items]
Total equity, beginning of period	$ 1,634,368	$ 1,423,727	$ 1,578,594	$ 1,354,933
Net income (loss)	73,856	68,414	178,695	175,303
Other Comprehensive Income:
Foreign currency translation adjustments	(91,222)	24,205	(112,488)	10,791
Pension and other postretirement benefit liability adjustments, net of tax	4,985	2,211	7,914	5,135
Unrealized (loss) gain on securities, net of tax	(2,567)	6,401	(2,491)	4,962
Unrealized gain (loss) on derivatives, net of tax	283	(994)	217	(885)
Total Other Comprehensive (Loss) Income, net of tax	(88,521)	31,823	(106,848)	20,003
Comprehensive Income	(14,665)	100,237	71,847	195,306
Dividends paid	(34,776)	(31,960)	(66,763)	(61,796)
Shares repurchased	(1,788)	(3,201)	(1,788)	(6,867)
Stock option exercises, net	4,956	261	505	2,662
Stock based compensation expense	(3,796)	773	1,904	1,482
Restricted awards, net	7,179	4,023	7,179	8,140
Total Equity, end of period	1,591,478	1,493,860	1,591,478	1,493,860
Total RPM International Inc. Equity
Stockholders Equity Note [Line Items]
Total equity, beginning of period	1,436,234	1,261,684	1,382,844	1,200,858
Net income (loss)	69,766	63,562	168,845	166,660
Other Comprehensive Income:
Foreign currency translation adjustments	(89,462)	19,409	(107,200)	2,338
Pension and other postretirement benefit liability adjustments, net of tax	4,374	2,200	7,134	4,961
Unrealized (loss) gain on securities, net of tax	(2,574)	6,341	(2,491)	4,909
Unrealized gain (loss) on derivatives, net of tax	223	(782)	171	(696)
Total Other Comprehensive (Loss) Income, net of tax	(87,439)	27,168	(102,386)	11,512
Comprehensive Income	(17,673)	90,730	66,459	178,172
Dividends paid	(34,776)	(31,960)	(66,763)	(61,796)
Other noncontrolling interest activity	51	(88)	47	(429)
Shares repurchased	(1,788)	(3,201)	(1,788)	(6,867)
Stock option exercises, net	4,956	261	505	2,662
Stock based compensation expense	(3,796)	773	1,904	1,482
Restricted awards, net	7,179	4,023	7,179	8,140
Total Equity, end of period	1,390,387	1,322,222	1,390,387	1,322,222
Noncontrolling Interest
Stockholders Equity Note [Line Items]
Total equity, beginning of period	198,134	162,043	195,750	154,075
Net income (loss)	4,090	4,852	9,850	8,643
Other Comprehensive Income:
Foreign currency translation adjustments	(1,760)	4,796	(5,288)	8,453
Pension and other postretirement benefit liability adjustments, net of tax	611	11	780	174
Unrealized (loss) gain on securities, net of tax	7	60		53
Unrealized gain (loss) on derivatives, net of tax	60	(212)	46	(189)
Total Other Comprehensive (Loss) Income, net of tax	(1,082)	4,655	(4,462)	8,491
Comprehensive Income	3,008	9,507	5,388	17,134
Other noncontrolling interest activity	(51)	88	(47)	429
Total Equity, end of period	$ 201,091	$ 171,638	$ 201,091	$ 171,638