Property and Equipment - Components of Property and Equipment (Detail) - USD ($) $ in Thousands	Apr. 30, 2021	Apr. 30, 2020
Property, Plant and Equipment [Line Items]
Total property and equipment at cost	$ 3,880	$ 3,411
Less: Accumulated depreciation	(2,089)	(1,368)
Property and equipment, net	1,791	2,043
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment at cost	1,748	1,543
Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment at cost	45	36
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment at cost	215	185
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment at cost	$ 1,872	$ 1,647