Commitments and Contingencies - Narrative (Details) - USD ($)	6 Months Ended
	Oct. 31, 2018	Oct. 31, 2017
Commitments and Contingencies [Line Items]
Operating leases, rent expense	$ 375,000	$ 306,000
Corporate headquarters
Commitments and Contingencies [Line Items]
Operating leases, rent expense	45,000	45,000
Laboratories and office space
Commitments and Contingencies [Line Items]
Operating leases, rent expense	0	58,000
New York laboratory
Commitments and Contingencies [Line Items]
Operating leases, rent expense	0	52,000
Rockville, MD
Commitments and Contingencies [Line Items]
Operating leases, rent expense	302,000	151,000
Gaithersburg, MD
Commitments and Contingencies [Line Items]
Operating leases, rent expense	$ 28,000	$ 0