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
	Aug. 31, 2012		Aug. 31, 2011
Numerator for earnings per share:
Net income attributable to RPM International Inc. stockholders	$ 33,913		$ 76,811
Less: Allocation of earnings and dividends to participating securities	(642)		(1,530)
Net income available to common shareholders - basic	33,271		75,281
Add: Undistributed earnings reallocated to unvested shareholders	1		4
Net income available to common shareholders - diluted	$ 33,272		$ 75,285
Denominator for basic and diluted earnings per share:
Basic weighted average common shares	128,805		128,094
Average diluted options	765		534
Total shares for diluted earnings per share	129,570		128,626
Earnings Per Share of Common Stock Attributable to RPM International Inc. Stockholders:
Basic Earnings Per Share of Common Stock	$ 0.26		$ 0.59
Diluted Earnings Per Share of Common Stock	$ 0.26	[1]	$ 0.59	[1]

[1] For the quarters ended August 31, 2012 and 2011, approximately 2,954,000 and 2,750,000 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.