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Financial Instruments - Financial Instruments and Balance Sheet Classification (Parenthetical) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Jul. 31, 2018	Jul. 31, 2017	Apr. 30, 2018
Investments Debt And Equity Securities [Abstract]
Obligations for which assets are held in trust	$ 125,400		$ 118,200
Gain (loss) on marketable securities	$ 4,001	$ 3,429

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Amount of unrealized and realized gain (loss) on investment in marketable security, excluding other-than-temporary impairment (OTTI).

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Amount of the liabilities for deferred compensation arrangements classified as other.

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