Income Taxes - Effective Income Tax Rate (Details) - USD ($) $ in Thousands	12 Months Ended
Apr. 30, 2021	Apr. 30, 2020	Apr. 30, 2019
Income Tax Disclosure [Abstract]
Computed “expected” income tax expense	$ 1,858	$ 1,428	$ 1,605
Increase (decrease) in income taxes resulting from:
State income taxes, net of federal income tax effect	323	214	339
Research and development credits	(640)	(703)	(678)
Excess tax benefits from stock option deductions	(641)	(737)	(251)
Foreign tax credits	(1)	(164)	(112)
Other, net, including permanent items	(140)	18	(65)
Income tax expense	$ 759	$ 56	$ 838

Amount of difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying domestic federal statutory income tax rate to pretax income (loss) from continuing operation, attributable to expense for award under share-based payment arrangement. Excludes expense determined to be nondeductible upon grant or after for award under share-based payment arrangement.

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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