Commitments and Contingencies - Narrative (Details) - USD ($)	6 Months Ended
	Oct. 31, 2017	Oct. 31, 2016
Commitments and Contingencies [Line Items]
Operating leases, rent expense	$ 306,000	$ 198,000
Corporate headquarters
Commitments and Contingencies [Line Items]
Operating leases, rent expense	$ 45,000	43,000
Lease expiration date	Nov. 30, 2021
Laboratories and office space
Commitments and Contingencies [Line Items]
Operating leases, rent expense	$ 58,000	52,000
Lease expiration date	Dec. 30, 2017
New York laboratory
Commitments and Contingencies [Line Items]
Operating leases, rent expense	$ 52,000	103,000
Lease expiration date	May 30, 2017
Rockville, MD
Commitments and Contingencies [Line Items]
Operating leases, rent expense	$ 151,000	$ 0