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Financial Instruments - Financial Instruments and Balance Sheet Classification (Parenthetical) (Detail) - USD ($) $ in Thousands | 3 Months Ended |
--- | --- | ---
Jul. 31, 2019 | Jul. 31, 2018 | Apr. 30, 2019
Investments Debt And Equity Securities [Abstract] |  |  |
Obligations for which assets are held in trust | $ 133,700 |  | $ 122,300
Gain on marketable securities | 1,945 | $ 4,001 |
Unvested obligations under deferred compensation plans | $ 17,300 |  | $ 24,600

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