Property and Equipment - Summary of Property and Equipment (Details) - USD ($) $ in Thousands	Jul. 31, 2017	Apr. 30, 2017
Property, Plant and Equipment [Abstract]
Furniture and fixtures	$ 76	$ 74
Computer equipment and software	917	872
Laboratory equipment	2,112	918
Assets in progress	141	472
Leasehold improvements	2	2
Total property and equipment	3,248	2,338
Less: Accumulated depreciation	(1,164)	(1,122)
Property and equipment, net	$ 2,084	$ 1,216