Commitments and Contingencies - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Jul. 31, 2016	Apr. 30, 2017	Apr. 30, 2016
Commitments and Contingencies [Line Items]
Operating leases, rent expense		$ 398	$ 304
Corporate Headquarters
Commitments and Contingencies [Line Items]
Operating leases, rent expense	$ 85	86
Laboratories and Office Space
Commitments and Contingencies [Line Items]
Operating leases, rent expense		105	83
New York Laboratory
Commitments and Contingencies [Line Items]
Operating leases, rent expense		$ 207	$ 136