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Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands | Apr. 30, 2021 | Apr. 30, 2020
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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 |  |

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