Income Taxes (Details) - USD ($)	12 Months Ended
	Apr. 30, 2021	Apr. 30, 2020
Income Taxes (Details) [Line Items]
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount	$ 1,000,000
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations	1,235,000	$ 36,000
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued	0	119,000
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense	(119,000)	$ 60,000
Research Tax Credit Carryforward [Member]
Income Taxes (Details) [Line Items]
Tax Credit Carryforward, Amount	700,000
Domestic Tax Authority [Member]
Income Taxes (Details) [Line Items]
Operating Loss Carryforwards	24,300,000
Deferred Tax Assets, Operating Loss Carryforwards, Subject to Expiration	16,400,000
Deferred Tax Assets, Operating Loss Carryforwards, Not Subject to Expiration	7,900,000
Tax Credit Carryforward, Amount	10,000,000
Domestic Tax Authority [Member] | Annual Limitation [Member]
Income Taxes (Details) [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards, Subject to Expiration	$ 3,400,000