Summary of Significant Accounting Policies - Narrative (Details)	12 Months Ended
	Apr. 30, 2022 USD ($) segment	Apr. 30, 2021 USD ($)	Apr. 30, 2020 USD ($)
Property, Plant and Equipment [Line Items]
Cash	$ 9,007,000	$ 4,687,000
Cash equivalents	0	0
Net income	548,000	362,000
Accumulated deficit	71,982,000	72,530,000
Working capital	2,200,000
Impairment of long-lived assets	$ 0	0
Number of reportable segments | segment	1
Unrecognized tax benefits	$ 181,000	181,000	$ 178,000
Income tax penalties and interest expense	0	3,000,000
Provision for (benefit) from income tax	$ 35,000	$ 75,000
Minimum
Property, Plant and Equipment [Line Items]
Useful life	3 years
Maximum
Property, Plant and Equipment [Line Items]
Useful life	7 years