7. Income Taxes (Details Narrative) - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2021	Apr. 30, 2020	Apr. 30, 2019
Deferred tax asset valuation allowance	$ 111,388	$ 118,137
Valuation allowance decreased	6,700	1,400
Unrecognized tax benefits from uncertain tax positions	0	0
Income tax penalties or interest	0	0	$ 0
Income tax penalties or interest accrued	0	$ 0
Federal [Member]
Net operating loss carry forward	$ 406,700
Operating loss carryforward expiration dates	2021 through 2038
Research and development credit carry forwards	$ 5,800
California [Member]
Net operating loss carry forward	$ 272,100
Operating loss carryforward expiration dates	2020
Research and development credit carry forwards	$ 3,300
Other state [Member]
Net operating loss carry forward	$ 900