Commitments and Contingencies - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Jul. 31, 2019	Jul. 31, 2018	May 01, 2019
Commitments and Contingencies [Line Items]
Discount rate	7.25%
Operating leases, rent expense	$ 239	$ 188
Corporate headquarters
Commitments and Contingencies [Line Items]
Operating leases, rent expense	24	23
Rockville, MD
Commitments and Contingencies [Line Items]
Operating leases, rent expense	151	151
Gaithersburg, MD
Commitments and Contingencies [Line Items]
Operating leases, rent expense	0	14
Rockville, MD New Location
Commitments and Contingencies [Line Items]
Operating leases, rent expense	$ 64	$ 0
Accounting Standards Update 2016-02
Commitments and Contingencies [Line Items]
Weighted average remaining lease term			7 years 8 months 5 days
Weighted average discount rate			7.25%