Reconciliation of Numerator and Denominator of Basic and Diluted Earnings Per Share, Calculated using Treasury Method and Two-Class Method (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended		6 Months Ended
		Nov. 30, 2015	Nov. 30, 2014	Nov. 30, 2015	Nov. 30, 2014
Numerator for earnings per share:
Net income attributable to RPM International Inc. stockholders		$ 83,433	$ 69,766	$ 183,248	$ 168,845
Less: Allocation of earnings and dividends to participating securities		(1,571)	(1,602)	(3,068)	(3,673)
Net income available to common shareholders - basic		81,862	68,164	180,180	165,172
Add: Undistributed earnings reallocated to unvested shareholders			6		18
Reverse: Allocation of earnings and dividends to participating securities		1,571		3,068
Add: Income effect of contingently issuable shares		1,354	1,340	2,706	2,679
Net income available to common shareholders - diluted		$ 84,787	$ 69,510	$ 185,954	$ 167,869
Denominator for basic and diluted earnings per share:
Basic weighted average common shares		129,398	130,028	129,723	130,061
Average diluted options		3,453	1,063	3,466	1,064
Additional shares issuable assuming conversion of convertible securities		3,883	3,875	3,883	3,875
Total shares for diluted earnings per share	[1],[2]	136,734	134,966	137,072	135,000
Earnings per Share of Common Stock Attributable to RPM International Inc. Stockholders:
Basic Earnings Per Share of Common Stock		$ 0.63	$ 0.52	$ 1.39	$ 1.27
Diluted Earnings Per Share of Common Stock		$ 0.62	$ 0.52	$ 1.36	$ 1.24

[1] For the six months ended November 30, 2014, approximately 3.0 million shares of stock granted under stock-based compensation plans were excluded from the calculation of diluted EPS, as the effect would have been anti-dilutive.

[2] For the three months ended November 30, 2014, approximately 3.2 million shares of stock granted under stock-based compensation plans were excluded from the calculation of diluted EPS, as the effect would have been anti-dilutive.