Commitments and Contingencies - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Jul. 31, 2017	Jul. 31, 2016
Commitments and Contingencies [Line Items]
Operating leases, rent expense	$ 102	$ 99
Corporate headquarters
Commitments and Contingencies [Line Items]
Operating leases, rent expense	$ 23	23
Lease expiration date	Nov. 30, 2021
Laboratories and office space
Commitments and Contingencies [Line Items]
Operating leases, rent expense	$ 27	26
Lease expiration date	Dec. 30, 2017
New York laboratory
Commitments and Contingencies [Line Items]
Operating leases, rent expense	$ 52	$ 52
Lease expiration date	May 30, 2017