Note 5 - Accounts Receivable, Net, Contract Asset and Contract Liability (Details Textual) - USD ($) $ in Thousands	6 Months Ended
	Oct. 31, 2021	Oct. 31, 2020	Apr. 30, 2021
Accounts Receivable, after Allowance for Credit Loss, Total	$ 3,566		$ 1,961
Accounts Receivable, Allowance for Credit Loss, Ending Balance	143		143
Contract with Customer, Asset, after Allowance for Credit Loss, Total	1,101		$ 421
Increase (Decrease) in Contract with Customer, Asset	680	$ 353
Increase (Decrease) in Contract with Customer, Liability	$ (4,553)	$ 2,141