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	$ 26,665	[1]	$ 76,811
Less: Allocation of earnings and dividends to participating securities	(479)	[1]	(1,530)
Net income available to common shareholders - basic	26,186	[1]	75,281
Add: Undistributed earnings reallocated to unvested shareholders			4
Net income available to common shareholders - diluted	$ 26,186	[1]	$ 75,285
Denominator for basic and diluted earnings per share:
Basic weighted average common shares	128,805	[1]	128,094
Average diluted options	765	[1]	532
Total shares for diluted earnings per share	129,570	[1]	128,626
Earnings Per Share of Common Stock Attributable to RPM International Inc. Stockholders:
Basic Earnings Per Share of Common Stock	$ 0.20	[1]	$ 0.59
Diluted Earnings Per Share of Common Stock	$ 0.20	[1],[2]	$ 0.59	[2]

[1] Restated

[2] 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.