Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Apr. 30, 2021	Apr. 30, 2020
Income Tax Disclosure [Abstract]
Federal net operating loss carryforwards	$ 36,340	$ 33,740
Foreign net operating loss carryforwards	4,064	3,307
State operating loss carryforwards	581	1,598
Federal and New Jersey research and development tax credits	3,303	3,076
Stock compensation	346	311
Accrued expenses	158	131
Other	545	595
Net deferred tax assets before valuation allowance	45,337	42,758
Valuation allowance	(45,091)	(42,431)
Deferred tax assets	246	327
Lease liability	246	327
Net deferred tax assets

Amount of deferred tax liability attributable to taxable temporary differences from lease liability.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121826272&loc=d3e32537-109319

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Amount, after allocation of valuation allowances and deferred tax liability, of deferred tax asset attributable to deductible differences and carryforwards, without jurisdictional netting.

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-Topic 740
-SubTopic 10
-Section 50
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-URI http://asc.fasb.org/extlink&oid=121826272&loc=d3e32537-109319

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Amount after allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible domestic operating loss carryforwards. Excludes state and local operating loss carryforwards.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible foreign operating loss carryforwards.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible state and local operating loss carryforwards.

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Amount, before allocation of valuation allowance, of deferred tax asset attributable to deductible temporary differences, classified as other.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible research tax credit carryforwards.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from share-based compensation.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from accrued liabilities.

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Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized.

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