Income Taxes - Effective Income Tax Rate (Details) - USD ($) $ in Thousands	12 Months Ended
Apr. 30, 2019	Apr. 30, 2018	Apr. 30, 2017
Income Tax Disclosure [Abstract]
Computed “expected” income tax expense	$ 1,605	$ 4,763	$ 7,565
Increase (decrease) in income taxes resulting from:
State income taxes, net of federal income tax effect	339	891	592
Research and development credits	(678)	(493)	(520)
Excess tax benefits from stock option deductions	(251)	(165)	(232)
Foreign tax credits	(112)	(211)	(170)
Rate change – tax reform	0	(1,206)	0
Other, net, including permanent items	(65)	83	(241)
Income tax expense	$ 838	$ 3,662	$ 6,994

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 excess tax benefit for share-based compensation cost.

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