Marketable Securities - Summary of Fair Value of Company's Investment By Type (Detail) - USD ($) $ in Thousands	Apr. 30, 2020	Apr. 30, 2019
Marketable Securities [Line Items]
Amortized Cost	$ 51,456	$ 68,365
Unrealized Gains	470	441
Unrealized Losses	(1)	(1)
Fair Value	51,925	68,805
Corporate Debt Securities [Member]
Marketable Securities [Line Items]
Amortized Cost	38,922	56,083
Unrealized Gains	295	405
Unrealized Losses	(1)	(1)
Fair Value	39,216	56,487
Obligations of U.S. Government and Its Agencies [Member]
Marketable Securities [Line Items]
Amortized Cost	12,534	12,282
Unrealized Gains	175	36
Fair Value	$ 12,709	$ 12,318

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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