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Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands | Apr. 30, 2020 | Apr. 30, 2019
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Income Tax Disclosure [Abstract] |  |
Federal net operating loss carryforwards | $ 33,740 | $ 32,025
Foreign net operating loss carryforwards | 3,307 | 3,641
State operating loss carryforwards | 1,598 | 1,653
Federal and New Jersey research and development tax credits | 3,076 | 3,315
Stock compensation | 311 | 486
Accrued expenses | 131 | 145
Other | 595 | 443
Net deferred tax assets before valuation allowance | 42,758 | 41,708
Valuation allowance | (42,431) | (41,708)
Deferred tax assets | 327 |
Lease liability | 327 |
Net deferred tax assets |  |

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