Reconciliation of Numerator and Denominator of Basic and Diluted Earnings Per Share, Calculated using Two-Class Method (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended				9 Months Ended
	Feb. 29, 2012		Feb. 28, 2011		Feb. 29, 2012		Feb. 28, 2011
Numerator for earnings per share:
Net income attributable to RPM International Inc. stockholders	$ 6,625		$ 1,097		$ 133,367		$ 118,884
Less: Allocation of earnings and dividends to participating securities					(2,441)		(1,869)
Net income available to common shareholders - basic	6,625		1,097		130,926		117,015
Add: Undistributed earnings reallocated to unvested shareholders					4		3
Net income available to common shareholders - diluted	$ 6,625		$ 1,097		$ 130,930		$ 117,018
Denominator for basic and diluted earnings per share:
Basic weighted average common shares	128,121		127,166		128,072		127,383
Average diluted options	2,256		2,276		555		637
Total shares for diluted earnings per share	130,377	[1]	129,442	[1]	128,627	[1]	128,020	[1]
Earnings Per Share of Common Stock Attributable to RPM International Inc. Stockholders:
Basic Earnings Per Share of Common Stock	$ 0.05		$ 0.01		$ 1.02		$ 0.92
Diluted Earnings Per Share of Common Stock	$ 0.05	[1]	$ 0.01	[1]	$ 1.02	[1]	$ 0.91	[1]

[1] For the first nine months of fiscal 2012 and 2011, approximately 2,618,000 and 2,111,000 shares of stock, respectively, granted under stock-based compensation plans were excluded from the calculation of diluted earnings per share, as the effect would have been anti-dilutive.