Commitments and Contingencies - Narrative (Details) - USD ($) $ in Thousands	9 Months Ended
	Jan. 31, 2017	Jan. 31, 2016
Commitments and Contingencies [Line Items]
Operating leases, rent expense	$ 297	$ 216
Corporate Headquarters [Member]
Commitments and Contingencies [Line Items]
Operating leases, rent expense	$ 64	43
Lease expiration date	Nov. 30, 2021
Laboratories and Office Space [Member]
Commitments and Contingencies [Line Items]
Operating leases, rent expense	$ 78	65
Lease expiration date	Dec. 30, 2017
New York Laboratory [Member]
Commitments and Contingencies [Line Items]
Operating leases, rent expense	$ 155	$ 87
Lease expiration date	May 30, 2017