Reconciliation of the Numerator and Denominator of Basic and Diluted Earnings Per Share (Detail) (USD $) In Thousands, except Per Share data	3 Months Ended
	Aug. 31, 2011		Aug. 31, 2010
Numerator for earnings per share:
Net income attributable to RPM International Inc. stockholders	$ 76,811		$ 68,996
Less: Allocation of earnings and dividends to participating securities	(1,530)		(903)
Net income available to common shareholders - basic	75,281		68,093
Add: Undistributed earnings reallocated to unvested shareholders	4		2
Net income available to common shareholders - diluted	$ 75,285		$ 68,095
Denominator for basic and diluted earnings per share:
Basic weighted average common shares	128,094		127,787
Average diluted options	534		467
Total shares for diluted earnings per share	128,628		128,254
Earnings per Share of Common Stock Attributable to RPM International Inc. Stockholders:
Basic	$ 0.59		$ 0.53
Diluted	$ 0.59	[1]	$ 0.53	[1]

[1] For the quarters ended August 31, 2011 and 2010, approximately 2,750,000 and 1,919,000 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.