Leases - Narrative (Details) - USD ($)		3 Months Ended			9 Months Ended
	Jun. 30, 2020	Jan. 31, 2021	Jul. 31, 2020	Jan. 31, 2020	Jan. 31, 2021	Jan. 31, 2020	Apr. 01, 2021	Jun. 01, 2020	Apr. 30, 2020
Lessee, Lease, Description [Line Items]
Operating leases, rent expense		$ 312,000		$ 240,000	$ 941,000	$ 717,000
Extension term		6 months			6 months
Operating lease right-of-use assets, net		$ 5,380,000			$ 5,380,000				$ 2,798,000
Gain (loss) on termination of lease					$ 75,000	0
Weighted average remaining lease term (in years)		7 years 11 months 23 days			7 years 11 months 23 days
Weighted average discount rate, percent		6.07%			6.07%
Corporate Headquarters
Lessee, Lease, Description [Line Items]
Operating leases, rent expense		$ 24,000		24,000	$ 67,000	71,000
Rockville, MD
Lessee, Lease, Description [Line Items]
Operating leases, rent expense		288,000		152,000	823,000	454,000
Operating lease right-of-use assets, net			$ 118,000					$ 3,800,000
Operating lease liability			125,000					$ 3,800,000
Incremental rent expense			$ 8,000
Rockville, MD | Forecast
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets, net							$ 3,300,000
Operating lease liability							$ 3,300,000
Rockville, MD New Location
Lessee, Lease, Description [Line Items]
Operating leases, rent expense		$ 0		$ 64,000	$ 43,000	$ 193,000
Operating lease right-of-use assets, net	$ 850,000
Operating lease liability	926,000
Gain (loss) on termination of lease	$ 76,000