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Marketable Securities - Additional Information (Detail) - USD ($) $ in Millions | May 31, 2020 | May 31, 2019
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Schedule of Available-for-sale Securities [Line Items] |  |
Available-for-sale debt securities, current | $ 7.6 | $ 8.6
Available-for-sale debt securities, long-term | 19.3 | 16.4
Equity securities | $ 87.1 | $ 87.5
Maximum |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments with unrealized loss, percentage of fair values less than original cost | 15.00% | 15.00%
Trading Securities |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Securities held in relation to deferred compensation plan | $ 9.1 | $ 12.3

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