Commitments and Contingencies - Narrative (Details) - USD ($) $ in Thousands	6 Months Ended
	Oct. 31, 2019	Oct. 31, 2018	May 01, 2019
Commitments and Contingencies [Line Items]
Discount rate	7.25%
Operating leases, rent expense	$ 477	$ 375
Corporate headquarters
Commitments and Contingencies [Line Items]
Operating leases, rent expense	47	45
Rockville, MD
Commitments and Contingencies [Line Items]
Operating leases, rent expense	302	302
Gaithersburg, MD
Commitments and Contingencies [Line Items]
Operating leases, rent expense	0	28
Rockville, MD New Location
Commitments and Contingencies [Line Items]
Operating leases, rent expense	$ 128	$ 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%