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Property and Equipment - Components of Property and Equipment (Detail) - USD ($)
$ in Thousands
Apr. 30, 2017
Apr. 30, 2016
Property, Plant and Equipment [Line Items]    
Property and equipment, gross $ 410 $ 418
Less accumulated depreciation (313) (344)
Total property and equipment, net 97 74
Laboratory Equipment [Member]    
Property, Plant and Equipment [Line Items]    
Property and equipment, gross 373 358
Office Equipment [Member]    
Property, Plant and Equipment [Line Items]    
Property and equipment, gross 31 58
Furniture and Fixtures [Member]    
Property, Plant and Equipment [Line Items]    
Property and equipment, gross $ 6 $ 2