Weighted-Average Actual Target Allocation of Plan Assets (Detail) - Pension Benefits - USD ($) $ in Thousands		May 31, 2020	May 31, 2019	May 31, 2018
U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Target Allocation		100.00%
Actual Asset Allocation		$ 516,550	$ 496,865	$ 487,233
Non-U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Target Allocation		100.00%
Actual Asset Allocation		$ 194,874	187,112	$ 188,960
Equity securities | U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Target Allocation		55.00%
Actual Asset Allocation		$ 261,000	295,100
Equity securities | Non-U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Target Allocation		33.00%
Actual Asset Allocation		$ 79,300	79,900
Fixed income securities | U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Target Allocation		25.00%
Actual Asset Allocation		$ 106,400	83,800
Fixed income securities | Non-U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Target Allocation		48.00%
Actual Asset Allocation		$ 88,200	79,300
Multi-class | U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Target Allocation		20.00%
Actual Asset Allocation		$ 118,200	78,100
Cash | U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Actual Asset Allocation	[1]	30,800	39,700
Cash | Non-U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Actual Asset Allocation		100	100
Real Estate | U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Actual Asset Allocation		$ 200	200
Real Estate | Non-U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Target Allocation		19.00%
Actual Asset Allocation		$ 27,300	$ 27,800

[1] The larger than target cash position at May 31, 2020 results from our February 2020 contribution to the RPM International Inc. Retirement Plan because of our plans to invest the February contribution over a period of time, due to dollar cost averaging.