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Common Stock - Narrative (Details) - USD ($)
12 Months Ended
Jun. 15, 2016
Apr. 30, 2020
Apr. 30, 2019
Class of Stock [Line Items]      
Proceeds from June 2016 Public Offering $ 4,300,000    
Payments of issuance costs $ 742,000    
Issuance of common stock for services     $ 6,000
Common Stock      
Class of Stock [Line Items]      
Issuance of registered shares (in shares) 2,000,000    
Share price (in dollars per share) $ 2.25    
Over-Allotment Option | Common Stock      
Class of Stock [Line Items]      
Issuance of registered shares (in shares) 258,749    
Consulting Services      
Class of Stock [Line Items]      
Issuance of common stock (in shares)   0 5,462
Issuance of common stock for services     $ 20,600
Accrued compensation costs     $ 14,600