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Marketable Securities - Additional Information (Detail) - USD ($) $ in Thousands | Feb. 28, 2019 | May 31, 2018
--- | --- | ---
Schedule of Available-for-sale Securities [Line Items] |  |
Available-for-sale securities, current | $ 7,600 | $ 97,400
Available-for-sale securities, long-term | 16,200 | 70,700
Equity Securities, Fair Value (Net Carrying Amount) | $ 89,200 | 144,555
Maximum |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments with unrealized loss, percentage of fair values less than original cost | 15.00% |
Trading Securities |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Securities held in relation to deferred compensation plan | $ 12,400 | $ 9,900

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